That's a key thing there. Show me any laptop from any other manufacturer, high end or otherwise, that doesn't have air vents on the bottom. I mean, it's crazy. The amount of Dell XPSs I've seen with busted motherboards because of overheating, and some of them cost more than a Macbook. Granted, they're known to have GPU cooling problems, but even so - you pay €1,300 for a laptop, you expect it to not require a motherboard replacement every year or so until the extended warranty runs out.
The Dell XPS 17" model and Inspiron 9400 is notorious for the GPU overheating anyway. 90% of faulty machines are due to blown GPU due to heat stress.