Different is good. It stands out. If it were to, say set up a full program, I can see the logic behind a loss. First, as has already been said, Miz is a heel and should be getting heat. However he does get cheered as well and that's a bit of a no-no.
Beating someone like Sheamus, especially in a surprise (but not really)cash-in, while he was down and out wouldn't get Miz any heat at all. People almost always pop for title changes and don't especially like Sheamus (which they shouldn't), making The Miz technically the "face" between the two.
Now examine if you will the opposite side of the heat/over coin. Besides getting yourself heat as a heel your job is to get the face over. In that way losing in an unsuspected fashion could be a great way of accomplishing it.
Say for example Randy Orton, who appears to be on fire these days, wins the belt and after his match is challenged on the spot by Miz. The crowd assuming it'll go down as it always has is pretty certain Miz is about to walk out the champ. But if he loses, it prevents Miz from getting cheered (either from the faux-surprised audience at large, or from the smarky rebels who like to cheer heels), and makes Orton look like even more of a beast. Thus it keeps everyone in their prescribed roles and could be the the foundation for a long term feud between the two.
Now, before someone complains: that'll "bury" The Miz. Let me say it won't simply becuase it's chapter 1 of the story rather than the ending of it. Miz can still be built up over the course of the feud. In fact the lose can act as sort of motivator now that he has to "prove himself" all over again and he'd be made to look legitimateperhaps even more than he did during the first encounterby the time the rematch roles around.
Is this the best way to do it? I'm not sure. Maybe not. But, it is at least one way to do it which actually has The Miz losing his cash-in attempt, preserving his heat, and really making the face in a big time way.