Nokoon,

My wife and I live in Indianapolis, which should have very similar weather conditions and have had an 06 since November. My wife does the bulk of our driving on her 50 mile commute with 50% Interstate with heavy traffic, and 50% winding state highways/city. She has been yielding around 44-48 mpg depending on the days temperature.. I assure you that she drives it pretty much like a normal car, probably the only "hypermiler" technique that she uses is to brake a little slower. Most of my driving is stop and go inner-city 1-2 mile trips and I have been yielding low 40's or upper 30's during my stints behind the wheel.

I assure you that the car will auto-stop when the temps are in the 20's, it just has to warm up for a few minutes before this starts to function, and yes it will not stop if the defrost is turned up. No matter how you look at it, these conditions will effect any car just the same. Our 99' CR-V can get close to 30 mpg in the summer, but gets much closer to 20 mpg in my wintertime city driving. A normal car is effected by increased heater/fan use, headlight use, defrost use, etc... as its electrical system is also charged by the engine/alternator.
If you are basing your decision purely on finances, you may be happier with the EX, depending on how much you drive, but we love our Hybrid, as it saves us money, and helps reduce our dependency on oil. Good luck, you will be pleased either way.