As Hawkfan2679 stated and olivecourt implied, there are no hard definitions of a spread offense. I typically think of a spread-team as one that primarily operates from the shotgun with 3 or more WRs and calls the majority of their plays from the line-of-scrimmage. All teams in the nation use this approach at times, but I think of a spread-team as one that uses this approach the vast majority of the time.
Based upon this definition, which of the Top 10 teams in the nation run a spread?
Oklahoma certainly does at times, though they are not afraid to bring in a TE or 2 along with a FB and go to a power-running game. I would probably characterize them as a spread team with the talent to be flexible and play anyway they want
LSU's offense is based more on the power-run game than the spread, although they do show good creativity out of spread sets.
Alabama is definitely pro-style, emphasizing the power-running game.
Boise State I would describe as multiple. They do everything, and they do it all well. Perhaps someone who has watched them more than me can tell me if they fit my definition of a spread team, but my sense is they are tough to pigeon-hole.
Standford was definitely a pro-style attack under Harbaugh, I haven't seen them play this year.
Wisconsin's offense will always be based upon a power-running attack.
OK St is definitely a spread team, as are Nebraska and Oregon, although they all do different things out of the spread. I don't know a thing about Texas A&M, can't remember seeing them play in the last few years.
So clearly teams can have a lot of success operating the spread as I have defined it, but they can also have a lot of success taking other approaches. Ultimately it comes down to talent and execution.
Having a creative offensive mind doesn't hurt, either. No matter what your base offense is, if you have the creativity and balls to throw a few change-ups here and there it always helps. The great teams always seem to have a couple of wrinkles saved for special occasions. This does not have to be a razzle-dazzle play where everyone in the stands can see that something unusual took place. Sometimes it is an adjustments of routes to take advantage of a certain coverage or a special screen to take advantage of a blitz. It seems like Chris Peterson from Boise is the master of this.