It sure doesn't take much to set some people off. This guy wants to buy a decent bit of kit and use it for Mame, and he's being told it's "absurd". Come on people.
We never know what is around the corner, so if you're buying a computer today you get the best one that fits your budget. I've never seen a case where buying a lower end machine has actually benefited anyone. And who knows what this guy will do with his machine in a years time, or two years.
Get a computer that gives you the biggest bang for your budget. If that means its over-speced for your current use, then all the better. You can't go wrong by buying something too fast - but you can if you buy something that eventually isn't good enough (as others have mentioned, perhaps in a years time the guy decides he fancies himself some Nintendo 64 etc.)
Let's not call it absurd. It's not absurd at all. There's nothing to say you should look at the minimum requirements for something, and then pitch the spec a couple points over. Relatively speaking the cost of a decent computer is small, and you'll buy a decent machine once and get years and years of enjoyment out of it.
Look for example at the work going on now to emulate discrete sound boards in older games - they will require a lot more horsepower. Just get it now and have fun.