At the page nine of the article Intel Core i5 2500K Linux Performance it's said
This is a false statement and should be corrected ASAP, as the untrue info potentially affects many Linux users. The K version is better for overclocking, but it has some features crippled compared to the non-K version. It lacks trusted execution and VT-d support. See the product details of the 2500 and 2500K, the Advanced Technologies table.There is also the Core i5 2500 non-K processor that retails for about $10 less than the K version, with the sole difference being the 2500K being an unlocked processor so it will be able to overclock better. If doing any overclocking, you are best off with the K variant.
Especially the latter might be a deal-breaker. VT-d support allows a host machine to share physical PCI devices to guest hosts when running KVM based virtualization systems. With the new Sandy Bridge K processors you can't do that. Many people might want to experiment with this features as it's supported by modern Linux distributions. But you need the non-K processor for that.
I guess Intel is crippling the overclockable processor because those interested in overclocking probably aren't interested in enterprise features (though people at this forum might make an exception to this assumption). This way they also prevent cheap-ass people from building servers with "too good" power/performance/price ratio using the over clocked K processors thus leaving room for their upcoming Sandy Bridge Xeons...