Okay, two things I'd like to address here.
First of all, I've just checked the size of the Windows folder of my computer. It's 25.4GB. That's for the entirety of my Windows 7 installation- loads of basic drivers for just about every system component and peripheral made in recent history, as well as a number of essential programs; everything necessary for a computer- which could be made of a ridiculously-wide combination of components- to run pretty much out of the box.
So why the hell does a console, with a highly limited number of known configurations, need nearly twice that much space for its "system" files?
Secondly, I think that a lot of console players aren't really understanding what consoles are these days. Guys, you're basically playing on cut-down, mass-produced, identical PCs... and console game devs are developing the same attitude PC game publishers have had for years: Get it out the door now; patch it later. And since you can't exactly update the disk the game came on, guess what? You need to download and install those patches. (And don't think that this "mandatory install" thing is just a craze that'll go away- it's only going to get worse as devs push the systems harder for prettier graphics.)
As a PC gamer, I've been dealing with this sort of thing for years. But it doesn't bother me, because I have five terabytes of storage in my computer (and another 2TB external drive for backups). I can put in and swap out as many hard drives as I please, and keep games for just about as long as I like. If consoles continue to be treated like PCs by publishers, but the console makers continue to try to lock down and limit their hardware as always, there's gonna be a logjam somewhere, and it's gonna cause problems.
Also, about the "100GB isn't 100GB" thing: You can thank marketers. To an engineer, a gigabyte is 1,024 megabytes- but to a marketer, a gigabyte is 1,000 megabytes. So when a hard drive with 500,000,000,000 bytes of storage is produced, the blurb on the box (made by a marketer) says 500GB- but your computer (made by an engineer) says 488.2GB. (And then of course there's overhead, bad sectors, etc.)