I agree that HPS seem to throw more heat.
It also depends on where your ballast is, and what sort of ballast, and if it is good condition- crappy ballasts run hot, it's a fact. Also I am starting to think that an aging bulb that is near the end of its life can cause the ballast to run a little hot... but the bulb I had problems with was 4 years old and should have been retired at 2, lol!
Also I want to say that light in the red spectrum is naturally more heat energy than in the blue... but I'm not any sort of expert and may be talking out my butt...