I don't know that the wheels would necessarily get hotter than the paint gets, but I do know that the conditions down there are a lot harsher than up on the rest of the vehicle. When you think about the puddles of road garbage and the brake dust and the slush and everything else that gets on the wheels, I just haven't seen it last very long.
I've done a lot of experiments with different paint waxes, sealants, and wheel waxes to see which works best. I've tried spray waxes, spray sealants, paste waxes, blended waxes/sealant pastes and polishes, liquid waxes and liquid sealants, and anything else I can come up with. I've polycharged and blended and mixed. Nothing has made a significant difference or demonstrated the ability to last longer than a couple of weeks.
My '05 Subaru Legacy GT was not the worst at attracting brake dust, but it did have issues with it. My Hondas just don't seem to have trouble, but with the Subaru I tried everything to try and make a difference. Nothing limited the amount of brake dust that accumulated, but they did make it easier to rinse them off and get clean wheels afterwards. ...at least, it was easier for a couple of weeks before they were right back to needing a wheel brush.
I used the inside of the wheel as my test bed since that was where they seemed to get the dirtiest. I waxed the whole rim, but I figured the inside would be the real test, so I took them off and got inside there too. I treated three wheels with different products while leaving the fourth wheel bare. I could never get pictures that demonstrated any significant difference in dirt accumulation between any of them. It is my opinion that waxing your wheels makes them look pretty, but doesn't offer any significant benefit in doing so. The labor required to continually wax them is greater than the labor required in scrubbing them, so I gave up with the wax.
