This is fairly primitive. The techniques used by tools like nmap to fingerprint operating systems were established in the early 90's by Comer, and they involve behavioral testing. You should assume that even if you modify all the files in your (say) Wordpress distribution, an attacker can still fingerprint it.
Even though this technique is primitive, how would you say it compares to the techniques used by run-of-the-mill comment spammers to identify and exploit outdated installations? Are most of them stopping at meta generator?
I doubt it's worth doing much more than looking at version comments in the HTML, because the majority of people won't go to the effort of hiding the version.
