It's true that website hacking remains a big issue in the spammiest areas of the web even though it's completely illegal. Unfortunately, there's a lot of unmaintained, unpatched web servers out there that blackhats exploit. It's fundamentally a hard problem, but we've been working on the next generation of our hacking detection algorithms.
I've always wondered why we don't see more startups offering hacker protection, detection, clean-up, etc. Companies like McAfee made a lot of money protecting personal computers, and there's a similar opportunity on the web server side.
I definitely agree with you that it is somewhat of an under tapped market, but definitely think it needs to be head up by the right individual(s).
To be sure there are many patched maintained web servers, applications that are also exploited (by someone for some purpose).
The best and the brightest get hacked and software maintained even by professionals regularly needs to be patched for new exploits. (Take Flash which seems to be running at between 1 and 4 updates per month). Or even OSX security updates.
I know everyone seems to think it's the other guy that doesn't have his act together and isn't following the obvious advice but there are many "other guys" that are quite capable and still end up having problems and being exploited. (Source: stuff that I read in news stories the same as everyone else.)
Focused exactly on what you mentioned (web site recovery, monitoring and protection).
*I work there :)