The major difference besides the disk drive is the data wheel which is only on the DGX202 and not on the DGX200/300/500. I'm not familiar with the DGX200 because US dealers can't buy the DGX200. These are sold only through the mass market stores such as Costco, etc. I would think that the DGX200 probably does not have the piano style keys as found on the DGX300 and DGX500 but rather the same synth type keys found on the DGX202. The DGX300 and 500 have a more "refined" look rather than the PSR type look of the DGX202. They are more designed to look like a piano rather than a keyboard. The other differences are that the DGX 300/500 do not have all the same functions as the DGX202 when using splits and layers. The DGX202 was designed more recently and has some important changes not included in the DGX300/500 which were derived using the PSR350's engine. It doesn't make them "older" just different features although very similar.
George Kaye
Kaye's Music Scene
Reseda, California