Once I asked a question. I recieved an answer but didn't like it entirely. I offered a bounty. The days went and I recieved no answer. One day I happened to go to the question and the previous answer had been substantially improved and I hadn't been notified.
I believe that notifying askers when an answer has been modified might be useful.
Of course, this has the downside that every little edit ( gramatical mistakes for example) might be annoying.
Nonetheless, this could be easily solved giving to the one who makes the edit the possibility to decide whether or not it is worthy notifying the edit to the asker.
What do you think?