Happened with the good old MB as well. I'll have to remember your response next time I have the chance to do so . Heh, my MBP's so hot even the magsafe is affectedi have a MB but mine gets preeettty hot sometimes too. so hot that in class i put it on a girls neck and made her scream int he middle of a lecture....pretty fun...
I dont the 85W rating is how much is actual power dissipation of the power supply, 85W should be the rated max that the it can supply and it'd be pretty bad if the MBP is running the power supply at full load. I'm not sure how much power the MPB consumes but it might be about 70W if it's an 85W supply. All power supplies get hot, packaging it in a small plastic case without any way of cooling doesn't help.Most power supplies are between 70 and 80 percent efficient, so 85W is about 75% of the energy being taken in, because 85W is how much is output. That's 113W taken in... minus the 85 given to the MBP leaves 28 wasted as heat.
28W is enough to get warm but nothing to be concerned about. The MBP uses 85W si move things and the spin things and switch transistors (lots of that), but in the end all 85 is spilled out as heat (or light).
The charger is therefore much cooler than the laptop itself, but has poorer dissipation so it can feel quite hot.