I think its really because they're not kept in a nice warm cellar and some don't have nice brown bottles to keep out sunlight etc, so if they're fresher they taste better. Also from what I know, aging beer a really long time is really only good for some types. I'm not an expert, but usually the big beers etc. In actuality after you've gotten past the "green beer" phase, beer is best consumed as soon as possible after that point. If not, it can get too much light exposure, etc and get skunked.