BS. how about travel? culture? academics? austin is far closer to berkeley or eugene or LA than knoxsville or bama. and let's not forget they are giving up oklahoma and USC, not exactly chicken feed competition.
"Cultural differences" are difficult as they are often ambiguosly defined and subjectively determined. However, most would likely find it easier to envision a Texan feeling far more comfortable ("being at home" so to speak) in Atlanta, GA than Los Angeles, CA. Or Gainesville to Corvalis. Or Oxford to Berkeley.
Of course, that's just my opinion which is based on my limited interactions with several friends who reside in Texas, and little else, but that which I think most would find reasonably agreeable.
Conversely, the travel argument is not so poorly defined, or difficult to determine, such as from your example:
Austin, TX to Berkeley, CA = 1,753 miles
Austin, TX to Knoxville, TN = 1,037 miles
+716 miles further to Cal than Tennessee
In fact, here are some other geographic / proximity notes of interest:
Greatest distance required to travel from Austin to a conference opponent?
Pac-10 (Oregon): 2,234 miles
SEC (South Carolina): 1,131 miles
+1,103 miles for Pac-10
Shortest Distance required from Austin to a conference opponent?
Pac-10 (Arizona): 893 miles
SEC (LSU): 430 miles
+463 miles for Pac-10
Average Distance required to travel from Austin to conference opponent?
Pac-10: 1,568 (incl. Colorado, which will be the second closest Pac-10 school)
SEC: 835 miles
+733 miles for Pac-10
Number of conference schools greater than 2,000 miles from Austin?
Pac-10: 3
SEC: 0
Number of conference schools greater than 1,500 miles from Austin?
Pac-10: 6
SEC: 0
Number of conference schools greater than 1,000 miles from Austin?
Pac-10: 9 of 11 (and Colorado, the second closest school, barely missed the cutoff at 967 miles)
SEC: 4 of 12 (and Florida barely made it at 1,106)
So, if either the allowance of individual television rights or geographic proximity to fellow conference members is important criteria (and, as an SEC fan, I hope and expect they would be) - the SEC seems to be a better, "fit" than the Pac-10.