I agree, it would be nice to have this opton in the user preferences. The reason its not is because when we started this forum a very long tme ago the forum software didn't do a lot of things we thouht important, so we ended up hacking the code to make it work the way we wanted. At the time this put us well ahead of every other forum system on the market.... but the world has moved on and we've not been able to update the forum software without sacrificing a lot of the modifications we made and which we now rely upon.
So the forum software is now pretty old and creaky and doesn't do a lot of things that people now take for granted -- like the email notifications. We took the decision a while ago not to waste resources working to continue tweaking this antique software, but instead to wait until the rest of the website upgrade was completed, at which point we will jump to a brand new forum platform too.
That point is getting closer... but it is taking a while as it is a very complicated upgrade and we have strictly limited resources available.
Technical Editor, Sound On Sound