When you answer the question at all, a message is generated in that user's "Recent Events" feed. So they are already informed.
The other side of the issue is a question of whether or not the community can really determine what answer it was that helped the OP the most, and the fact is that the cannot. The community can vote up answers to indicate which answer they this is the most useful in general. So if your answer is more generalizable, or more abstract, thereby making it applicable to more situations, then you answer will be highly voted up. It doesn't mean that you answer was 'more helpful to the OP'.
Votes mean 'useful in general'
Accepted means 'useful to me'