Isn't this pretty much business as usual for Valve? I think you're vastly underestimating how much of this stuff already goes on in Windows, they aren't some small outfit just dabbling around in Linux. I'd be very surprised if a few enthusiasts hacking around surprised them at all. If anything, they may take it as a sign that lots of linux users want to run Steam and take it more seriously.
You are wrong. A bunch of hacker-kiddies does not signal interest in games on linux... it signals interest in linux hacking games (hacking inthe sense of cracking).