I share your pain as well, everytime you have to play the game another process runs and it slows your game down. Luckily I'm gonna buy it for the ps3 as well.
plus you don't need nearly as much memory to run it.
If Steam saps enough memory to slow your games down the PC you're trying to play them on isn't fit to play games in the first place.
I have a rig I built for ~150-200 dollars. I managed to scrounge up a Socket 939 dual core, 4 gigs of brand new DDR400(Probably 70-75% of what I paid for it

), an 8800GS, a full ATX SLI-capable motherboard to run it all in and a terabyte or so of harddrive space. I run a garbage picked CRT that can do 2048x1536, the rest of input/output devices cost no more than 30 bucks(360 pad was 20 off eBay, mouse 15 from Walmart, keyboard 25 from Walmart, speakers 30 from Walmart). I spent less building my rig than I would have on either console, yet it's capable of running today's games just fine. Crysis, GTA IV, BC2, Fallout, they all run wonderfully.
My rig doesn't even feel Steam when I'm in-game. Hell most of the time I can even leave Firefox running, even though it loves to gobble up 200-300MB of ram for no reason. If your rig is in any way fit to run New Vegas it won't even notice the miniscule amount of RAM Steam uses.
I'm still kind of anchored to the whole physical copy thing. It just makes it feel more secure,
Then buy your Steam games on Retail DVD. You still get the DVD you seem to tie to actually owning the game. You don't have to buy Steam games from the Steam store to use Steam for your games. You can buy every Valve game ever made on an actual DVD, as well as most third party Steam games. New Vegas is one such game.
Best part is that if something happens to the disc you don't have to torrent an ISO or buy a new copy. You don't really need the disc for anything. It speeds up initial install a bit, and it makes a fancy coaster.
Steam is currently the best platform for digital distribution with its unlimited free downloads to any PC you log your account into, disc free gaming, achievement/stat tracking and automatic patch updating I really have no clue how someone can hate on something that is so much better then everything else available and is free to use.
Here Here!