Culturally. The only part of the country where the NFL is bigger than college is the north east. College football has 6 stadiums over 100,000 capacity and 13 total larger than the biggest NFL stadium. Huge populations descend on towns like Lincoln, State College, Ann Arbor, Tuscaloosa, Knoxville etc. It's a way of life, not just a sports team.
But let's not derail this thread. If you want to discuss it further let's go to the college football thread.
Those stadiums are bleachers not individual seating which skewers the numbers. Colleges look to cram as many fans into a stadium as possible to maximize revenues while the NFL is an entertainment business and must accomodate fans much like other professional sporting leagues, entertainment industry, and cinemas do. NFL cannot go around building 100,000-seat stadiums for multiple reasons, one of which would be selling tickets with the high costs to attend, the other being the construction cost restrictions as they are funded differently (I do not see colleges with billion dollar stadiums for various reasons). College football is geared towards attendance like a family reunion while NFL is geared towards televising - they're business models are much different. Both are massive tailgaiting experiences too.
Very few schools have stadiums exceeding 60000 seating capacity, and most that do are the biggest and most attended/funded schools in the country, while all NFL stadiums top 60000, some former pro stadiums or Olympic venues; indeed most schools cannot 1) afford such venues, and 2) sellout regularly. Does anyone really believe Kentucky would have 100000 attend college football games on a weekly basis? How about Rice, or New Mexico State, or Duke?
Yes college football is woven into the local fabric and the fans often have a connection via current enrollment, alumni, lifelong fan, or sponsor. I find it fascinating and it's probably the closest Americans can get to what it's like to be a European football fan; there's also an abundance of raving lunatics that support a college/conference. I would certainly have a stronger connection to Texas had I attended the school but I'm just a fan that chose them as a kid. Same with the Cowboys as growing up in Fort Worth my family were diehards and thus I became one as well. College football ranked well behind NFL, MLB and NBA for most of my family and friends. I suspect it would have been different had I grown up in Austin.
The NFL is bigger in terms of revenues, ratings, viewership, etc., which must amount to something. The NFL is bigger than college football in metropolitan areas like Dallas-Fort Worth, Denver, Houston, Oakland, Pittsburgh, even small-city Green Bay not just the northeast. If the NFL wanted to place teams in small cities like Green Bay, in a relative short time the team would sink into the fabric of that location as well. However, that is not economically feasible in today's climate but the league did begin in that fashion (Canton, Green Bay, Rochester, etc) until westward expansion began in all sports. Colleges are the staple of a small city/town while NFL clubs are located in vast metropolitan areas with far more on offer than a small city/town has to offer, which is rather fascinating that a big city club/team can gain a strong foothold against what is on offer culturally and entertainment wise. It's rather easy being the big fish in a small pond, like Gerrard would tell you.
NFL games routinely dwarf college football ratings. A few weeks ago, Denver/New England had a 15 share nationally while LSU/Florida had 4.7 for a 3:30 start time (and not directly televised against one another either). Regionally the LSU/Florida game drew half the viewers than Miami/Cincinnati that same weekend... yes, Miami/Cincinnati. Another example is the BCS title game is now on a cable network - the Super Bowl would never leave a primetime network, and is often the highest viewed annual event on US television.
If 100000 bleacher capacity stadiums are the trump card then I suppose NASCAR is even bigger with more than 100000 attending race weekends. Even MLS tops attendance numbers of NBA and NHL and many MLB games - does this make the MLS better? Not at all.
Another thing - playoffs decide the champions not voters/computers telling fans who should play for a mythical national championship. Nor is there a bias towards certain conferences/divisons in the professional ranks. How NCAA has carried on for decades with this fraud of a system is a joke. And because of this we have seen historical conferences destroyed/bloated with schools jumping around to better their revenue streams and help create this conference bias we see today. One might retort that colleges do not relocate and unfortunately this does happen in pro sports, however only six times since the AFL/NFL merger has this occurred and the last was in 1997. I do not like it but this happens in all industry.
While I find college football fun to watch, most games are utter dross and often venture to the four-hour territory and the overall quality of play is nowhere near the NFL level. But being a distant second is not a bad thing.