Well no, it's the others things, the godmode, the custom items, that aren't technically hacking. They're just cheating, and the major difference there is that people do it for their own benefit. And if someone wants to make his game boring by turning on godmode, why should you care? It doesn't affect your game unless you like to play with random strangers you don't know. And even then it just means having some immortal buddies. It's not like they can kill you in D3, given that there's no PVP. Play with your friends whom you trust to not cheat and there is no problem at all. But getting your account hacked and your characters stripped bare, that's a big damn problem for you.
While the use of cheating may just be "cheating," the back end of how it works is closer to hacking than the use of keyloggers to compromise accounts. While it is possible, I haven't seen anything to indicate that, at least for the last several years, all compromised accounts in WoW (and now D3) haven't simply been the result of customers practicing poor computer security.
Although, if they compromise online accounts that way, why they don't also target personal financial information is a big question. Maybe they do but it's less obvious, because financial businesses don't have online forums where their customers publicly complain. Maybe they don't because it is harder to target - there are a lot more financial institutions than MMOs, and certainly many more avenues to 'focus' infection through compromising ads via online gaming sites, or the sites' users database (and then trying those user names and passwords on the games the site covers).
If the black market for accounts and items have compromised the network security of Blizzard and any number of other online games, but admins won't admit it, then that's an interesting quandary. Actually, I think RIFT actually had that problem and admitted it, after fixing it, though I don't know how much the trading still continues. I don't have a stake in these sort of games any longer, but personally I still believe the weakest point of security is still a PEBKAC error.