It goes both ways. I don't think its fair to assume that all 21-25 year olds are to blame for increased prices on micros. Sure, there will always be the "yuppies" who drink micros because they make you look cool (sophisticated, different, classy), but there are also a great portion of us who are out there because the beer is good. $9 a six pack is a lot to pay to look cool, especially for a low profile micro (Parker36 had it dead on --> if you're going to "look cool" you're going to do it with a known beer, not too expensive, not Keystone water either, but something like Sam Adams). Also, who hasn't turned 16 and wanted to get out and drive? Who hasn't turned 18 and wants to buy a lotto ticket or a cigar (even if you won't smoke it). The point is, when you turn 21 (college yuppie), you are going to buy beer. When you become passionate about beer (thats why I brew), you want to experience the options. My friends and I sometimes have beer night. We all buy a six pack of whatever micro, and pass bottles around. Why? Not to get %$#@&# up, but rather to experience the world of beers. Call it being amateur drinkers, but I wouldn't call it a yuppie fad. As far as I have seen, there are just as many "elders" as there are "yuppies" who either enjoy beer or do it for buzz. Its what I call...an "unjust stereotype".
As far as increasing prices...I would blame inflation and most definitely the shortage of hops (the good ol' factor of supply and demand and how it can drive up prices!)