What, because even sportscasters nowadays are speaking of the point spread? Brent Musberger is the best for letting you know who he's got money on that day, particularly if it's a BS TD that is irrelevent to the game that gets him a cover... or vice versa. You can just tell... "Well, the Trojans with another touchdown running up the score." Or "what a big confidence boosting touchdown for the Illini." Something of the sorts...
Right now I'd say the number is only around 10% holistically. But probably closer to 70% during the end of college basketball season because of all of the office tournament pools and such, not to mention the actual gambling itself on each individual game.
The ABC noon college football game is probably 10% would watch something else if not for gambling... the ESPN2 game at noon is probably 90% would watch something else if not for gambling... you get my point