Plato wrote: "What could be different, hmmm, let me think, maybe it's the extra digital processing required for surround sound...." But there is no additional digital processing required. For DVD-A, there may be the added pass through MLP but that is entirely lossless. For SACD, there is probably less processing than for standard PCM. (Notice, I am not including DD or DTS as they are currently used in this consideration.)
Thus, I believe you are looking for an excuse for a spurious observation. There is simply no reason for multichannel to be any less highly resolving or satisfying than stereo and, in good practice, it is not. It simply has to be done right and, frankly, it will cost more for 5.1 excellent channels than for 2.
Kal