I hate to break it to you, but you don't own your games.
Due to how copyright law works, when you play ANY game, listen to ANY music or watch ANY movie, you are simply paying to have a licence to use that media. You do not own that media. Technically, licenses can be revoked, even for physical discs (i.e. patching your console to no longer let you play X game).
If you actually owned your games, you would have copyright authority over them, and could freely distribute the game, sell it, etc. As when you own a piece of media, according to law you technically own the intellectual property of it. So that's why all media you purchase is just licensed to you instead. The games you play on Steam are as much yours as the PS3 version. Just because you use a disk doesn't mean you own that game, you just own a license to use it (just like Steam).
Nonsense. In all cases before software appeared you owned the
copy of whatever was on your media, be it a record, CD, book, etc. You could do as you pleased with this, except for copy it to other people. You could still give it to them, take it apart, rearrange it, etc.
Software companies seem to think it's an ethical practice to prevent people from doing this in most cases. It's garbage and most of what they write in EULAs should be illegal. Some of it is, and that's why nobody gets busted for reverse engineering. The reason they can do these things is because they arrange it so they won't agree to give you a copy until you agree to their terms. This doesn't mean similar terms apply to all copyrighted works.
Requiring Steam is silly. I don't agree with it; I never have and I never will. However, I do like Steam. I find it extremely convenient to use. I also had Skyrim ready to play the minute 11/11/11 happened. No hanging out in silly stores and putting another box on my shelf to waste space.