(a) I don't agree that that's what I'm going to be spending money on in two years, or that costs will have fallen that far for the entire box (CPU, RAM, yes; physical box, PSU, no), or even that that money will be available (I'm in Ireland - check out the news on our economy :) Right now, whether it's better to keep euros in the bank or to spend them while they still have purchasing power buying things that will last and can be used seems like a terrifyingly close decision!
(b) This box's destiny is to go sit in a room quietly and just work. Any time I spend on it after it's in that quiet room is time wasted, and I'm willing to spend a bit more (though not a huge amount more) now to save a lot more then. If I was a postgrad again and my time was low-cost and I wasn't hosting data I really worried about, sure, I'd pick the newest, shiniest toy and try to make it work and if it didn't, oh well, I learnt something; but that's not the case here, I just want a solid box I never have to worry about no matter what else we throw at it. This ain't the project car in the garage being endlessly worked on for fun, this is the family estate wagon that's used for the shopping and getting the kids to school, if that analogy makes any sense.