Temperature changes make a big difference. I experienced that while I played, and again while I was in the Marine Corps. Running in North Carolina when it's 65 degrees, then going home on leave to run in single digit weather is quite a difference. To think otherwise is naive, or SEC homerism. There's a reason everyone ran their PFT in the summer when I was stationed in Maryland.
Where are these girls in bikinis on the beach in December/January? I live in Florida, right on the beach, and I can tell you the locals aren't running around in bikinis when the temperature drops even below 80, let alone 60. If it drops into the 60's, you're talking about parkas and snow gear.
Call me crazy, but I always thought they should be focused on what they're doing, not how much and what kind of partying they're going to be able to fit into their schedules.