I really don't get this "inconvenience" thing, but then I've had Steam installed since 2003, so for me registering Civ V was basically "open window, type code" - you know, like game installers have been asking PC gamers to do since time bloody immemorial. If the additional step of installing a file is too much for you (additional, that is, to the process of installing a whole bunch of other files) then perhaps you should put Civ V back on the shelf - it's too complicated for you. Perhaps Dark Reign is more your style. Or Halo Wars.
I've been playing online since about...1995? I've used a *SHIT-TON* of online game clients, and most of them sucked nadgers, and tried to bury themselves in your system. Steam is - this incident notwithstanding - generally very reliable, unintrusive, doesn't hog your system resources, and, if you're an online gamer, is genuinely very useful. Even without the friends system, automatic patching, free DLC, game invites, trading, the mental sale-time deals, community, forums and so on, it would be worth installing for the Steam overlay alone. That thing is genius, as is being able to run it over non-Steam games.
It's had moments when I've been frustrated with it, but after over 8 years I'm still on it, so it must be doing something right.