D'oh!

Okay, here are the calculations again, using my best estimate of your winter/summer numbers - there is no good data (ie 10 degree data) for the Accord, and there are no real high-temp tanks for the Ranger, but here goes:

Xcel's Insight 'Per Mile' Gas Cost
============================
Summer (106 mpg): $0.0225/mile (1/106 * $2.39)
Winter (72 mpg - a whopping 32% hit!): $0.0332/mile

Xcel's Ranger 'Per Mile' Gas Cost
===============================
Summer (42 mpg): $0.0569/mile
Winter (34 mpg - a measly 17% hit): $0.0703/mile

Summer Savings, Xcel's Insight Over Xcel's Ranger: $0.0569 - $0.0225 = $0.0332/mile
Winter Savings, Xcel's Insight Over Xcel's Ranger: $0.0703 - $0.0332 = $0.0371/mile

So,

Xcel's Insight saved him more money in the winter than in the summer (over his Ranger, even though, as he correctly points out, it took a higher-percentage FE 'hit' in the winter than the Ranger)

___Follow the math … just follow the math …

Perhaps way, way up in Minnesota and points north things wouldn't work out like this, but I think the vast majority of citizens in the continental US can refute the argument that hybrids do worse in winter than non-hybrids. I also think your numbers are probably a 'worst-case' set, as you are pushing the temperature-sensitive aspects of the hybrid (ie the battery) farther than almost anyone (that's a compliment ).