It would have been nice to have had even a glimpse of MK on the video, just to show that he was involved, but not even that! I'm very disappointed indeed! 
I totally agreed with you!
Sure, we all know that he was involved, but I must admit that I have problems to recognise him playing on the record.
I think is was one of these "email sessions", where Mark just records something. I can't even understand why Mark does these, just for the sake of it? I can't understand playing for a guy on the record, and the guy don't even know you, you've never met. Obviously, that's done for promoting reasons only.
It's not exactly the case with "Stand By Me", but in a way, it really is. Mark promoted the thing, nobody said he will be a big part of it.
