I agree that this can be unreliable. Just take a look at your Add/Remove programs if you have any doubts.
Mine thinks I use 7-zip rarely, Open Office rarely, and Eset Anti-virus rarely, when in fact all three are used every day of life. It also says I use Microsoft Office frequently, when in fact I only ever use Outlook ('cos I use Open Office as my default .DOC, XLS and PPT application).
If I relied on this information, it would suggest I should uninstall everything except Office, when in fact this is the one thing I could easily do without.. If I decided to bin Office I can use the company Web Mail, Thunderbirds or Evolution (Yes it also runs on Windows
http://www.dipconsultants.com/evolution/features.htm )
Which licensed products are you trying to check?