If you compare laptops with comparable desktops (not just Apple) you see you pay for that all in one design for the battery and more that the desktop doesn't have.
No offense intended but have you just begun to use a computer and shop for them?
So, I'm sitting here dreaming about my next computer... comparing laptops and all in one imacs. Honestly, the $1799 iMac looks to have much the same capabilities as the $2499 MacBook Pro... other than the obvious fact one is portable and one is not. Aside from double the Hard Drive size in the iMac, and double the RAM in the MacBook Pro... both use the 2.4GHz Intel Core 2 Duo.
The only significant difference, performance wise, is that the ATI Mobility Radeon HD 2600 XT may be a bit slower in performance than the NVIDIA GeForce 8600M GT.
Am I missing something here or is there a $700 premium your paying here, just for mobility?