diablo 2 was beatable for me on all 3 mode with out cheats like hero editor D3 will be no differant just might take longer to beat it since there will be no cheats
it is my understanding that diablo III will be online server/client model similar to world of warcraft, albeit without the persistant online world (think of darkspore). therefore, your items, your gold, the monsters, your health, basically everything that could be 'cheated' will be server side and inaccessible. it's possible someone might make speed hacks or some such thing, but those will be basically useless.
i think you are going to find that diablo III doesn't have the same limitations Diablo II does (i.e. internet connections are fast and there are tons of server space) so they can make a 'server client' game that appears to run in 'realtime' and yet can keep cheaters from ruining it.
the fact that it had MP coop to it and that it is blizzard led me to believe this is going to be like warcraft with battle.net controlling your items/currency and then individual servers (similar to warcraft raids) being created for SP and MP game 'instances'.
too bad, really. i mean purists will love that they can play the game and nobody has any advantages. which i agree with in the MP domain. but SP players who loved to tinker with the game or wanted to MOD it OR just plain want to finish the game in a controlled or 'fun' way and see all of it's content, will just have to play it over and over or for weeks on end. the game had better be pretty 'interesting' and 'evolving' to have any kind of SP base to it.
i think D3 is going to be no trainers, no SP hacks. all the hacks will come from black market online people who will risk banning your account or worse and unfortunately the emphasis will be on MP use.
my 2 cents... we won't know until we see a demo or actually see the game or HEAR blizzard tell us this..
best,
mike