This was intended as a comment, not an answer. But I was too lazy to divide this into separate comments - since it is too long - and I also think that in this way it is more readable.
Feel free to edit this, if there are some inaccuracies.
I wanted to check for myself whether there are many bumped old question. (For the sake of simplicity, let us say that old means older than 7 days.)
I went through 150 recently active questions (as of this moment; timestamp shows 2012-09-26 18:26, of course I've spent some time typing and formatting this text).
I found out - to my surprise - that 8 old questions were bumped because of a new answers:
(The names of the links are numbers of questions, but I've put here links directly to answers, that caused the bump.)
Some of them were edited after being bumped by a new answer - but I would not count these questions. (I consider this a natural approach - if some thread was bumped anyway, why not improve it.)
I found 9 questions bumped because of an edit or a retag:
Of course I might have made a mistake - I don't know of a better way how to do this than to go through questions manually. But anyway 9 questions out of 150 does not seem as a large number to me. (The fact that several old questions have new answers was more surprising to me.)