I don't really have any problem with this. Unlockable/downloadable content is content you pay for, regardless of whether it is on the disc to start with or you download a file from Xbox Live. What difference does it make? You are getting something that wasn't advertised or included with the initial game release. When you buy the DLC/UC, you get something no one else has unless they pay for it too. Seems fair to me.
Now, whether this type of behavior is innappropriate or, in other words, "likely to piss off the gamers," is a completely different question. Obviously, judging from the furor on these boards, most gamers don't like this type of behavior from a publisher. I don't have a problem with what Capcom has done, but clearly most do. So I would say it was not their smartest move. But I don't think ther is anything inherently wrong with it.