Luddite gave a good description of the differences.
The 2200 design is simply a refinement of the 2100 design. Both machines work similarly and cut beautiful mats. Both machines are durable and require little maintenance.
I guess the 2100, which was produced for quite a while, may be the most popular straight-line mat cutting machine on the planet. As such, parts probably will be available for a good long time. Hope so... I have a 60" model 2100 in my shop.