You're right, sort of. All of this expansion has little to do with things that happened 25+ years ago, but about how you're doing now, and more importantly, how many people are going to tune in on TV and watch you.
Washington has four titles, only one of which is recognized by any real source - USA Today/Coaches, and none are recognized by the AP or other commonly accepted sources. By these standards of using obscure ranking sources, Oregon and TCU were also national champions last year, Missouri and USC were in 2007, and Boise State won in 2006. They also did not go to a bowl from 2002 until 2010, and have not won a Pac-10 title since 2000. Sure, we don't have such a resume in our past, but if you put us head to head over the last 10 years, it's a far more even comparison.
Syracuse, much the same, has success from even farther back. Sure, Ernie Davis is a legend, and his Heisman win is a huge accomplishment for the program. That Cotton Bowl win over Texas was also huge for the program - in 1959 when it happened. But the ACC did not say "Oh wow, they won a Heisman and a national title 50 years ago, we can't pass this team up." If that were the standard, the ACC and the Big 10 would be lining up to take Army.
In terms of success on the field, unless your program is legitimately a blue blood, your isolated year or two of success from 25 years ago is not going to be much of a factor in expansion. Syracuse was not taken by the ACC for their football accomplishments on the field. They were taken because of a large alumni base in NYC who will flip on the TV. And make no mistake, they don't flip on the TV to watch Syracuse football first.