I remember asking a question in one another technology site (I forget now) when I was building a computer and I stated an issue with heating. I provided the temps of the CPU, but people responded that they couldn't tell if its normal or not without knowing the ambient temps. That is if its a 100f degrees in my un-airconditioned home office, then having having the CPUs running hot is obviously a factor of outside temps and inside heat generation.
I have my rMBP on a stand, I'm not sure if it helps with the heat but it does guarantee the air vents are clear of crap on my desk