Ultimately they serve two different needs and therefore two different markets. For one person the Macbook is a no-brainer, but for someone else, the Razer laptop is a better choice.
The use of a dual-core CPU instead of a quad-core CPU should cover most of the cost of the GPU upgrade, which means that either Razer's trying to make a lot more profit per machine than Apple's flagship laptop, or Razer's getting screwed on the cost of a bunch of commodity components.
I would liken the gaming PC to an audiophile hi-fi setup, almost no one expects it to fit in a messenger bag and run off a battery. For the connoisseur, no portable setup will fulfill all of their needs, and in all likelihood, they'll have setups to cater to each use case. But what if you can have a machine that's ultra-portable, but could also be docked to a setup that allows for high frame rate/high res gameplay? Some people already do this on laptops with express card bridges to external PCI-E sockets. Works pretty well. Here's an example of one such build, although I've seen better:
http://www.techradar.com/news/computing-components/graphics-...
For me, the real $150 premium that makes the MacBook Pro justified is the fact that it runs OS X. For hardcore gamers, that's not really a plus. Also, the optical drive is a "meh" at best.
On the other hand, the Razer will offer a much better GPU and will be $150 cheaper than the high-end MPB 17".
It's hard to compare machines built for such different specs, but I'd say the $150 premium on the MBP is more than justified.