This article basically gets it right judging by what I have seen - in short, if you were not providing computers, communications, or x-ray screening products, then you didn't see much in the way of increased purchases of tech-sec products after 9/11, at least in the USA.
I believe that I can actually generalize even further based on my (admittedly unscientific) polling of tech-sec product companies by saying that 9/11 vacuumed up budgets to pay for extra personnel-related charges (e.g. overtime pay) and to procure screening equipment (e.g. the aforementioned x-ray machines). The confusion that resulted from merging lots of componets into the new DHS (Department of Homeland Security) further locked up RD&E as well as Production procurement budgets, most of which have not returned to pre-9/11 levels for the many small businesses across the USA. Finally, the major security-defense contractors got big integration contracts, which pulled even more money from small tech-sec businesses.
So, contrary to popular belief, the last few years were not kind to small businesses in this field. The good news for them is that it looks like this situation is changing.
(Author's note: edited for clarity after initial post - blogging on too little sleep!)