i've had a ton of wet races and it seems to depend by track. i assume by the ones that are harder on tyres. as I've had several like you guys race saying where i was painfully off the pace at the end.
Last night did 2nd race in Malaysia in my second season(50%) and it was heavy rain all race. I started pole and finished first by not pitting and changing tires. Alonso, Vettel, Webber, and Hamilton all pitted with 7 or 8 laps to go. None of the midpack or read guard teams pitted. The ones who did pretty much split on finish. Alonso and Hamilton took 2nd and 3rd but the rest fell back behind the mercs and saubers.
They definitely had performance drop on par with mine with the tire wear. Perhaps the weather changed and i just didn't notice it/hear the engi call it to me during the race as i haven't really seen it happen other than that one instance.