Because it was so easy to find items via auction house, Blizzard saw no need to give, say, rare or legendary items a reasonable drop rate. I'd heard and seen firsthand accounts of people getting no such items after 4-6 full playthroughs. I'm not even talking GOOD items, I'm just talking any item of decent rarity at all. However, because of how easy it is to actually trade and sell items on the auction house, if the drop rate were the same as it should be in a single player game, the auction house would be absolutely flooded with the stuff.
Me, I generally prefer to abstain from anything that will take away fun from a game. I see no need to do something as efficiently as possible if that takes the fun out. The auction house removed fun from the idea of finding your own items, but it was impossible for me to find items on my own. So, I got to act 2, and then gave up on the game. My skills were crap (I was a wizard, I had like 2 good attacks), all the items were either terrible or things I couldn't use, everything was just pretty garbage. And, I tried this game when Torchlight 2 wasn't even out yet. I'd rather play Torchlight 1 of all things than Diablo 3, because that at least was fun. Not hard, but god, you at least got places in it without everybody else's garbage helping you out.