I wouldn't exactly break it down into the hard divisions like was done above but those rankings are somewhat subjective and can only be a relative indicator. It is unlikely that the #25 class is as talented as the #1 class. However it isn't unlikely that the #7 class is better than #1 or that #12 is better than #7.
USC's rankings aren't written in stone either. Along with very good recruits, they've been well coached and benefited from a conference that still hasn't caught up. In any given year, only one or two teams will seriously challenge USC. Further, California has alot of great HS players... and alot more media density than say South Carolina or Mississippi. IOW's, being from California, Florida, or Texas will usually move a kid up the ladder a little compared to a player from Kentucky or Tennessee.