@ LadyCrimson: Your latter reason is why I tend to avoid PC gaming, but for New Vegas I'm making an exception because I want to try and make a machinima in addition to having access to a large array of mods. I do remember hearing that Steam was pretty bad in its early days, though, so it's good to know it's improved since its inception.
Enforced patches aren't (or weren't) common to singleplayer PC gaming. It's mostly Steam (or similar services) or always-online games that tend to make worldwide changes at a constant rate, that do that.
Also, my digital download copy has no issues with mods/GECK etc, so no concern there if you're wondering. The mods do make the game much more fun/long-lived, imo.
If you buy the physical copy, you will be able to install from the disc and forgo the long download.
Yes, that's a reason for many. Also ISP download limits are another valid reason. Don't have limits and my connection had me ready to play in an hour, tho, so it's not that big a deal. And later you can 'backup' your Steam game and reinstall from that so no big download (tho you do have to be in 'online mode' to do it), which means only thing you have to download are the patches.