The least they could do is begin loading the game during the countdown. Halo does it. Call of Duty does it partially (That's why their maps load so fast if you didn't know). Gears of War loads the map as you're spawning...though for this type of game that'd be bad.
I mean seriously, how hard would it be to load the map during the countdown, even if there's no check ready. Or maybe have both!
Load the map during countdown, and if everyone pressed ready by the time it loads, then the game starts! Even if the countdown's still at 30 seconds!
Also, a veto system would be nice for winter/summer maps, for slow computers to say "NO!" to the winter map.
Edit: Not saying I would vote "Yes" cuz I love the winter map honestly. I just know a few friends that lag like crazy on it.