How do you people manage to use that much space? I model, have music, and uncompressed .AVI videos of gameplay and I'm still on the low end.

Well, in my case I have a fair bit of programs and a lot of heavy games downloaded. I also have about 20-30 1920x1080 high quality videos on my D: drive, some of which are an hour long and some others are just 5 min shadowplay videos, but all the downloads do add up over time.
It all comes down to the person.