the biggest difference is the ability to record digital audio through usb which gives pro quality recordings entirely independent of the quality of your soundcard, or whether you even have a soundcard at all.

The 2100 has added usb data transfer to the 2000, but you need a computer connected... SD storage is reasonably cheap, self contained, and can hold digital audio as well as 1000s of midi or technics files without the need for a computer connected or a boxful of floppies to swap.