High megapixel count, extremely fine detail, just all around goodness.
QUOTE
As with film, due to the increased size of the imaging chip (up to twice that of a 35 mm film frame, and thus as much as 40 times the size of the chip in a typical pocket point-and-shoot camera) they deliver more pixels than consumer-grade cameras, and have lower noise. Features like fan cooling also improve the image quality of studio models.
Looking at film frame sizes:

Imagine the 35mm box is the size of full frame DSLR sensors.... the rest of those boxes are medium except for the 5x8 is large. The two cams linked above are the 645 size.