You can't use 2 separate reviews for comparing 2 different things (ie. here's a review of a GTX 480 and here's a review of an HD 5870, neither one having the other in it. The 480 got 80fps in some bench, and the 5870 got 400fps in the same game, therefore the 5870 is OBVIOUSLY vastly superior). And the same goes for heat/noise comparisons. If a chart doesn't have both cards, you can't draw conclusions that 88 degrees (ALMOST 90!!!!) is just BARELY under the 480's 93 degrees, because in the same situations (case, ambient temp, stressor, etc.) the temperatures for each could be off. You can't one-to-one them like that.
Yes, the HD 5870 is not the quietest/coolest card ever. Everyone knows that. But the plain and simple truth is: The GTX 480 takes significantly more power, (~40%) and gives off more heat, (~40%) and runs hotter, (few-several degrees) and is louder than the HD 5870. Whether or not this matters to you at all, completely up to you. Where the point of "too much" noise and heat is, is a totally personal thing, unless cards are actually, seriously dying before ~6 months.
Is that clear, yet?