I still have the spreadsheet open, so here we go again:

Prius 'Per Mile' Gas Cost
============================
Summer (48 mpg): $0.0498/mile (1/48 * $2.39)
Winter (42 mpg = a 13% hit): $0.0569/mile

Corolla 'Per Mile' Gas Cost
============================
Summer (35 mpg): $0.0683/mile (1/35 * $2.39)
Winter (30 mpg = a 14% hit): $0.0797/mile

Summer Savings, Prius over Corolla: $0.0683 - $0.0498 = $0.0185/mile
Winter Savings, Prius over Corolla: $0.0797 - $0.0569 = $0.0228/mile

=> Driving a Prius saves you more money (over a Corolla) in the winter than in the summer (23% more, with the numbers given)

Did you expect it to do that? Your comments seem to indicate that this example would 'seal the deal' in your favor.

Maybe I'm reading you wrong, but I'm not sure why you seem bent on refuting this. As I said at the outset, it just seems like hybrid owners wilt under the argument that their cars' advantage shrinks in the winter, (heck, I felt that way at first) when in fact, in many, many cases, they actually do better. Even your Accord example was tipped only about 5% in the Accord's favor - and I still maintain that your numbers are far from typical due to the way you squeeze every last bit of advantage from the Insight's battery.

If the issue all along was with my 'equal-percentage FE hit' assumption, well, I'll give you that - but I showed how it could still work with the hybrid taking a much higher percentage hit than the non-hybrid. (I'll probably go back and take out that assumption altogether, and just replace it with with 35%/20% hybrid/non-hybrid respectively).

Sorry if I've taken this all wrong...