1) It depends on the games...in some cases you ARE missing a lot of content. The Console version of Baldur's Gate has nothing to do with the PC version and is a sad sad mockery. If you're into RPGs, then I would personally say you'll probably find more content, particularly with older games, on the PC. But that's gradually changed at the console games have become more sophisticated. As an RPG PC-player, I would say yes, there is probably more content on a PC simply due to the fact it's easier to make content more accessible, both to the system and the user. BUT, given that I am not an active Console-player, this may no longer be the case and you aren't missing out on much.

2) Mods can be a form of cheating. Mods can also be a way of adding content to the game, either intended but not released content, or new content. for example, there are NWN2 mods that insert dialogue and plot that was omitted from the final release, but included in the installation's data so you could at least know what it was. There are mods out there that now insert these aspects into the game, albeit not as well as they would be if the developers actually used the material in the first place. There are also mods that exist that add entirely new plot lines or dialogue into games (the Gibberlings3 mods for Baldur's Gate come to mind). There are also mods that exist to fix bugs the producers didn't, increase access to items or area, improve the UI, you name it, there is probably a mod that does it. They're just user-created alterations to games. If a user can do it, then it can be a mod.

3) Online PC games, in my experience, have a very limited cheat profile, mostly because developers take the time to keep the playing field level between players. Games that are not online can have anywhere from no cheats to cheat lists many many pages long (particularly when you include lists of items, feats, exploitable scripts, etc...) Many games I've played have a debug function that exists to help players fix bugs (like item X didn't drop when it was supposed to, or you get stuck in an area and need to move your character to another area or spot on the map), but these scripts are obviously exploitable for cheating purposes. Oh the wonders you can accomplish with a keyboard


I hope that answers some of your questions...I don't do much console gaming so I can't really compare well, but I've done PC gaming since green-screen Apples, so I at least have a clue there