I can tell you why this ends up being the case. Perhaps you can get a clearer picture (as will deanjo... ) of what I've been trying to tell people off and on in the forums.
Unless the studio and publisher take it upon themselves to make a Linux version (Id, until recently Epic, perhaps Valve (which might change things if they do come our way...)) you have to find a publisher that is willing to allow a port to be done for a given title. Not all publishers do this (see: Atari...) and when they DO allow it, they're interested in a royalty up-front and then one for producing a production run of SKUs for the new version. The production one is due for each production pass and MUST be paid before you can legally sell the game in question. The right to port royalty, the one that you pay to even get a sniff of the game's source code, is typically anywhere from $10-250k per title, paid up-front. The average that LGP pays is on the order of 10-15k, half down, half upon completion, in preparation for mastering. Sometimes this is more, sometimes this is less. When you wonder why we don't have more AAA titles, it's because they want 50k and up just to see the code- and this doesn't get into what they want out of you per unit.
Now... You're down 20k on a "good" title already. On what would be considered a 'sane' mastering run for Linux, this translates into an immediate $7 per copy charge up-front for the FIRST batch of 3000. You can eat a bit of this by making a larger run, but at 10k units (which is insane...) it's still $2 per copy.
At 3000 units, the mastering costs, including packaging, will most likely run you $1-2 per disc, box, and manual, if you're frugal on the packaging. Let's presume you choose the packaging like what the big-boys use. $2.
Now... Development costs. If the studio does the work, it's typically nothing on that part. If you have to have a port team or a consultant (like Ryan Gordon or myself...) do it it'll cost money. Me, I work for a little less than Ryan does because it's not my main calling right at the moment (not for wont of trying, mind...). Doesn't make it any less work, etc. If you use the typical effort and costs, this translates into $2 or so per unit sold in costs.
Right now, we're at $11 for an older, but nice title- not a new one of B grade or higher. And we've not got into the royalties owed and that it needs to at least show enough of a profit to carry it forward. Typically, they want $3-5 per unit, sometimes as high as $10 per unit at this level of sales.
At this point we're hovering close or past that threshold you're talking to for Jack Keene. For something a bit older than this title. If you want something like Rage from Id this way...heh...the price goes substantively higher.
When you all compare the stuff you do, you're neglecting the detail that you're not buying a Linux SKU specifically made by a seperate publishing interest or one working specifically in concert with the mainline publisher (which would be the case with most of the more modern MacOS titles...), you're buying a Windows SKU, built and published for Windows with an installer thrown in as an afterthought for Linux or pulled from off the 'net in the same manner.
When you run that way, you're not voting Linux either, really. But they're supporting us all the same (well...until recently, that is...) so it's sort of okay because they're using other metrics to justify their support. Other studios, on the other hand, don't use "installed base"- they go strictly for what they think will make them money. Windows. Until they see that they can make money doing Linux SKUs, even if it's unofficial and hackery-pokery'd like Id's stuff, you're not going to get any better than what you're seeing right now for some time to come.
The only way to do this is to buy what IS available so that places like Runesoft and LGP can hand sales numbers to studios and publishers to get simultaneous deals like the MacOS crowd have now. The main reason why they have those sorts of deals is because they have the sales numbers on titles to get the attention of publishers and studios- to give the OS a serious look at least. All we have right now is people begging, hat in hand.
GDC was a sobering experience for me. They thought we were laughable. They still do, actually, for the most part. A fringe of people that insist upon using that "server" OS.
I can sympathize with the porter's cost issues (except for packaging - let me download it, I don't even want a box; heck, I even get my groceries online), but I will not pay extra for a Linux version of a game. I got into Linux a year ago substantially because I could buy my 1st computer & save $500 by using various free software equivalents. The big "selling" point for me (besides virus immunity) was cost savings. It's a bit of a slap in the face to be presented a higher price for a game now. The # of potential Linux-using buyers may be small, but the # of potential Linux-using buyers who are idealists willing to pay a substantial Linux-market-share-growth premium must be even smaller.
I don't dual-boot (MS didn't get a cent from me when I built my system) & don't necessarily require Jack Keane, so if it weren't available for Linux, I wouldn't require Windows. There are enough good FOSS games, games from id software et al. that work with Linux, & Wine works well enough that I don't need Keane so much that I'll pay a premium for it. That's strong competition, & you have to compete with that. In fact, there are already more games than I have time for.
Before anyone bitches about gamers that bitch about the price for holding back Linux gaming, consider the negative effect of providing software that costs more than the Windows alternative. Hardly a way to attract new converts.
By the way, Frictional Games made Linux & Mac versions of all 3 parts of its (excellent) Penumbra series, & offered them at the same price as the Windows versions. Now they've gone & offered a great discount - ONLY FOR MAC & LINUX! Needless to say, I went & bought the lot
I'll buy Linux software, you just have to make it attractive.