I think you are right! I checked my firewall and DW was blocked - after unblocking it I was able to run Web Assist extensions. And in my opinion this is a fundamental problem. I personally don;t think once you have bought and registered the product you HAVE to be connected to the web to use it.
There does seem a proliferation of software products that now insist on registration via the web, probably because of security/pirating. I personally work in many regions of the UK, travel and 'live' in hotels + I have a base in rural Spain - therefore Internet Connection is not 100% reliable or available yet I still like to work/develop sites using my Dev laptop / server set-up.
I also used to work for a UK Bank's IT dept' on an internal network (INTRANET) where (for bank security) we had no Internet connection on the Dev' machines and always needed to install via disk or flash mem after a rigourous procedure of anti-virus scan/red tape... (nothing happens quickly in banks !! ). I guess your very useful Exts maybe wouldn;t work in a similar setup ?
As a gloabal supplier of software I guess Web Assist should expect this ?