As a casual player, I've never personally agreed with need before greed. I work my hiney off to be able to buy/earn/farm for gear. That being said, the beauty about DKP is that the casual player still has a chance to get items, because once the Full Time Raid Force people get their gear, the casual people can still get theirs. Yes, it may take several raids, but I've seen incredible stuff rot because there were no takers.
I firmly believe in DKP as I have been in other guilds where I have gotten royally screwed over in loot despite my full time participation. I've also liked DKP because even if I'm low man on the totem pole, when a zone becomes farm status, I can still get drops on occasion. NOTHING is worse then spending 1000 hours in a zone and still not having an armor set, because your guild leader is afraid that if you have a full set, you won't come back (like the rest of my class did). I *still* did an additional 500 hours of farming *after* I got my set, which is more than I can say for *anyone* in that guild at the time, other than the raid leader, of course. ;)