And for the sake of argument:
I need offline single player. Not only do I often travel to places without internet access, where I still need to kill some time and even now play Diablo 2 because it's nice bite-sized entertainment, but even at home the internet is flaky and often drops, sometimes for hours on end. It's, as far as I know, not an uncommon situation in my country, especially in smaller cities and towns. So... what do I do? Not buy the game? Or get better internet, possibly by starting my own god damned provider?
Mods are the only reason I am playing diablo 2 right now. I've been playing MedianXL, it's not perfect, but far, far better than the original Diablo 2 or LoD. I've heard the same about other mods, like Eastern Sun and what have you. Furthermore, Diablo 3 seems to be simplifying a lot of things for accessibility, but accessibility does not interest me personally (heaven's sake I'm posting in Dwarf Fortress's forum), and modding in some more advanced features (crafting in MedianXL, for example, or the uber-quests) would add to my positive experience.
Even without that, a great part of Blizzard games is the custom content, wow be damned. Come to think of it, a lot of the greatest or at least most popular content EVER has been mods. Counter Strike, that Mech Warrior crysis mod, even DOTA? Yeah.
The auction house... I'm not really sure. On one hand, it allows players to circumvent development and item acquirement, which is always stupid and should be discouraged. Microtransactions may be the future, but I don't have to like them, and even if I did, it'd be if they were trading convenience and visual diversification, not pure power. I read on the SA forums that because someone earned the item it's different... well, no, it's not. Does someone want to buy stuff to get powerful quicker? Yes. Will there be stuff regardless of the source? Yes. And don't delude yourselves, there will be plenty of the more powerful items, even with the cap on free transactions. Perhaps even more, because if you know you can only offer so many items per week, which ones will you offer? Will this give those players an advantage over someone who does not want to/cannot afford to buy items? Yes.
So what difference does the source of these items make?
One positive side of this is that Diablo 3 doesn't seem to be a pvp focused game, but I'm a petty person and knowing someone else has gotten something I'm proud of (an item drop, to be precise) for a few bucks which he can afford, because he doesn't live in a country where the average salary is 400 euros per month, makes me angry. See? Petty x] That's why I'm listing it as an advantage!
On the other, it's pretty interesting as a social experiment and something to observe from afar. I'm pretty certain this market will face some fascinating phenomena like bubbles, collapses and what have you. And since everyone in the games industry still has that wonderful "HEY GUYS BLIZZ RELEASED SOMETHING WHERE'S MY COPIER", we could be in for a lot of in-game real money trade in the future, thus setting an even larger experimental field.
And yeah, there are separate auction houses, but if you just got a really powerful item that you can't use, yet someone else would really like, where would you sell it? Sure, it depends on what uses gold has, but I think I can still guess quite accurately.
The really sad part? Even with all my whining, I'm likely to at least try the freaking game