I also think it depends on the size, but I don't understand, that people recommend a 6ft x 2ft hutch with a 6ft x 4ft run for 2 rabbits, but the same size for 3? Is that right?
I think 3 rabbits can lay down together as well as be seperate in a 6ft x 2ft hutch, and I personally wouldn't have a problem with keeping 3 rabbits in a hutch that size, as long as they weren't really big rabbits.