The difference is, all of them actually *do stuff*. What does Steam do for me? Takes up RAM and CPU cycles.
What does it do for you?
For one, it lets you play your game even after the dog chews up the CD, your disk drive burns out, or your whole damn computer explodes five days after you accidentally sat on the disk and shattered it into a thousand pieces.
It provides updates IMMEDIATELY after the publishers release them, without having to hunt them down from whatever site they run with their bogged down servers. Sure, you could do it yourself, but it's convenience.
When a new game comes out, you can get it BEFORE it is released, and sometimes for LESS than the retail store price! In today's world economy, a little break in the wallet-expenditures can help out a lot.
There's more, too... but it's all stuff you'd have to actually have -used- it, to know about... because it's a program that highly personalizes itself to the user. If you don't use it, it can't offer you anything. It's the same way with people who -hate- DVR... you really have to get to know how it works before you condemn it across the board.
As for your complaints:
Right now, I have Steam open. It's using exactly 25,224 K of ram. That's WITH it flashing advertisemants for sales and all my online friends and new, upcoming games. Do you know how INSIGNIFICANT that is? Firefox alone is eating up more than 200,000 K. My 'svchost.exe' files eat up 30,000 K a piece. Hell! Windows AUTO-UPDATE is using more, and I have auto-update DISABLED!
CPU cycles? It's currently using precisely ZERO here... and I've got New Vegas running in the background!
The people decrying steam have only -two- valid arguments, and they sure as hell isn't MEMORY usage or CPU cycles or serving no purpose.
If you want to complain legitimately, argue about the regional-copy rules and the needing to activate the game online once. At least those points are semi-defensible.
Do you want to know why people come out defending Steam so fiercely? It's because the people who -hate- it so much and try to make it out to be the devil... can't even be bothered to LIE well. The arguments they use are so lazy, unimaginative, and -old- (your complaint about RAM and CPU dates back to the earliest iteration of the software) that people who don't even LIKE it all that much can't help but call [censored].
I'm not about to go run out and write thank you letters to Valve... but it's a decent program with a good idea for an otherwise bad situation, and it does it's job.
So yeah.
Like I said. Tell me how it feels on the high ground... I'll tell you how great Skyrim is.
Fair enough?