Internet Problems. Some have a rather sub-par internet connection, making Steam game access rather sporadic. This is also a valid argument. But offline mode exists for a reason. One can play games without any internet connection required.
Did I miss anything?
Yes, you did. You missed why a sub-par internet connection is a problem.
My Steam screwed up, and would not let me install from disc. I had to restart installation dozens of times. (And I mean dozens, I would be surprised if it wasn't 50 times)
So I attempted to download the game. That would have taken 20 hours at my internet connection. I left it running all day, and then I left it running overnight.
Or so I thought. My computer went into a powersaving mode because I had been a numpty and not switched that off. Thankfully it was at this point that the "from-disc" installation worked.
Then it had to download the latest patch before I could play, which took 5 hours of constant internet connection.
So it turned out to be two days from when I got the game to me almost being executed.
Now of course, I can play offline or online, it doesn't really matter. The reason I will quite happily avoid buying any game released in the future from Steam is that I spent the best part of 12 hours screwing around trying to get access to a game that I legally owned the rights to play, and what was more, that I actually had in my possession. Furthermore, for me personally, Skyrim was my reward for completing my end of year exams, so I had been focused on my exams for two weeks and ignoring Skyrim in order to play Skyrim on the weekend after my exam. All my friends were still doing exams, and after exams people don't really want to do anything strenuous anyway, they just want to plonk out and relax. So for me my end of exam celebration was instead spent effing around with Steam.
Let's just compare this to a non-steamworks game. I could have gone to the shop, bought the game, come home, installed it on my computer and be playing it at most 1 hour after I got home. I would be more likely to buy a copy of a non-steam game than a steam-game.
Do you see the problem?