1 - price difference is often $10 between the 2500 / 2500k
2 - some people don't want to OC if the CPU can do the job just fine, they will OC once performance falls below par
3 - 2500k will probably have a better price on the used CPU market since it can be OC
That's what I am doing. I just have turbo on (with low voltage), but I'm not using my 4.4GHz OC until I have to. Besides, I don't like high voltages, since I'm going to be using this CPU for a few more years.