You're right. The Dell is better.
In the end you can't (yet) stick a quad core CPU with a high end graphics card into a small chassis with a single cooling source, the technology just isn't there yet -- the thing will run hot, and as a result the lightweight airplane will periodically attempt to achieve lift off ;-)
The Dell will of course run hot as well when under load, but the cooling system is superior, the net effect being a quieter work environment (compiling from source is a noisy affair), which is far more important to me than anything the MBP offers.