Space.Not rediculous at all - necessary. How do you think they can make a mobile Mac only 1 inch thin? Socket would force the whole thing to be significatly thicker. It's a brilliant design decision not "rediculous".
I'm not sure I buy that explanation. I've opened up my M1710 and the socket isn't nearly tall enough to stop Apple from employing a similar design and still keeping their 1" thickness. The reason the Dells are thicker is because they use fairly large heatpipes and fans to cool their laptops.
Edit: While on that subject, speaking hypothetically, would someone with a Rev. A MBP be able to purchase a Rev. B MBP mainboard/CPU and put it in their system? If Apple kept their internal design consistent then at least that would be one way (albeit extreme) to upgrade.