It has more to do with location then anything else.
The SEC and ACC cover the southeast where states like Florida and Georgia produce a ton of talent.
The Pac 10 covers California and USC usually cleans up as far as 5 stars.
Northern states usually don't produce near as much talent (as far as high "star rated" players) as the west coast or south in football. I would assume Ohio State pulled most of the 5 stars for the Big 10.
The recruiting ratings are really nothing more than a popularity contest. I've seen how some recruits number of stars changes after they commit, some go up and others go down. Tom Osborne rarely got any 5 star recruits but he won more than 80% of his games over a 25 year period and fielded some of the most dominant teams in history. Many great athletes get overlooked by recruiting services, especially if they come from small town schools. There are 3 states that produce about half of the top players, California, Texas, and Florida. The recruiting services focus on those and other metro areas and often times don't even bother to check out top players from rural areas.
I've followed recruiting for about the past 5 years or so. If there's one thing I've noticed its the fact that coaches are a lot better at evaluating talent in comparison to recruiting sites.
For example my Penn State Lions recruited 2 quarterbacks last season. One was given 5 stars by Scout while other was given 4 stars. The 4 star recruit is our current starter. Just like the NFL draft a lot of these guys are unpredictable.
In fact, you'll notice that a lot of the guys who move on to the pros were actually 3 and 4 star recruits. I don't put too much stock in the rating system. Coaches know exactly what types of players they want to go after.
Ohio State is always good at developing corners. Malcolm Jenkins was only a 3 star recruit and he went in the first round. Chimdi Chekwa is Rivals number two ranked defensive back according to their power rankings. They also gave him 3 stars as a recruit.
Developing talent is as important as recruiting raw talent.
Star ratings are funny things. The more schools that make offers, the higher the stars creep. Less schools means less stars. Choose a smaller school over a bigger school and your star rating drops. Keep in mind that the star ratings are not about how they are going to perform in the college game. They are about pro prospect potential. Somthing often 5 years away dealing with kids who have not yet become men. It's an estimating crap shoot.