I hardly remember Hilton much as a freshman (maybe that's the point!) and I only caught Nolan a little in one of the exhibition games, but I will say that Nolan has nowhere near the kind of beef and talent (yet) that most likely pushed Hilton a lot.
When Hilton was a freshman, he was practicing against Emeka, Marcus White, Hayes, and heck even Justin Brown! There's a little bit of everything in that group of guys.
Then they bring in Boone, Charlie, and Nelsonian!
Hilton units aren't made, they're born (Wait a minute. Strike that. Reverse it.).