Not always.
The insurers only have a stacked deck on an OVERALL view. You can still "win" if you happen to choose a vehicle that turns out to have an exceptionally bad service record.
For example I'm sure that the majority of people with extended service contracts on 1989-1996 Chrysler minivans with the infamous Ultradrive A604/41TE transmission in it did in fact benefit since very few of those vehicles passed 100K miles without a trans rebuild. Of course, if you looked at Chrysler minivans - all models - as a whole over that time period, the insurers would still have come out ahead - but far less profitably than over model lines.
Naturally, if you do in fact choose a model that turns out to have an exceptionally bad service record, you lose in some fashion because it's going to be in the shop more than your driving it.
If you are one of these new car buyer that simply must have the latest car models with the newest and least-proven engine and transmission designs in them - like for example the first generation Priuses - why then you probably are making a good financial bet with an extended service contract.
Very stupid auto purchase in all other respects, but at least you will probably get your money's worth out of the service contract.
Ted