You can always buy a USB number pad for data entry tasks, but you can't remove a numpad from an existing keyboard. A 3rd party number pad is probably higher quality anyway.
This sacrifices a number of portability bonuses that laptops usually bring. Try finding a place to put a USB laptop on a flight, or finding space to put it on one of those small student desks that has less surface area than the laptop itself.
No way, then I'd have to deal with that annoying cord all over my desk and then having it invariably get tangled in my backpack. It's not that big of a deal to have a slightly offset keyboard.