Nasty weather is probably the single greatest contributor to wear. In ideal weather, nice parts will probably do a little better in the long run, but when you factor in abuse it doesn't make sense financially to spring for top-shelf stuff - especially if you have to leave the bike locked outside and/or unattended.

Like 2wheeledsoul and pinkrobe said, maintaining the bike is key. Chasing bearings around is not my idea of fun yet, but it seems like every year I get more involved in working on my bikes. From that perspective I prefer older stuff since it's less fussy and cheaper to replace. With ebay, craigslist, etc... it's easier than ever to find parts to keep an old bike running.