Much better for whom exactly?
It is safe to say that a very large percentage of all future sales will be for portable computers. In the case of an Apple Powerbook, having to carry around a USB key is not only impractical, but it also means you lose 50% of the available USB ports just so you can run the operating system.
A USB key is small enough that you can leave it plugged in all the time, and if you're carrying around things to plug into the USB ports, you can carry around a USB hub too.