The answer is that most printers are optimized for PLA, but can usually be setup for ABS also, but the big difference is that to print ABS you need a heated bed, machines with a heated bed can obviously print both, and that goes for other materials of which there are a wide choice, dissolvable and flexible, nylon etc.

In summary if you buy a printer without a heated bed then you cannot print ABS. ABS is a more tough material, so depending on what you want to print could have a bearing on what printer you buy.

Printers with heated beds that I know of are reprap machines, the Makerbot Relpicator 2X, also the Ultimaker, hope that helps.