I dont think that the hub is allowing those speeds.. my guess is that the router is buffering the IP packets for you there by creating a caching effect.. The best way to see if this is happening would be to run a throughput test on the LAN itself. Download something like iperf,
http://dast.nlanr.net/Projects/Iperf/, and give it a try. Basically it will blast tcp packets from your 'server' to the host and record a very accurate measurement. Place one of the computer on the Router and the other behind the hub and see what type of speeds you get..
I will try this in lab tomorrow.. I have a Cisco 515e and an older Intel 10baset hub that I could give it a shot.. Here is why I think that this is happening.. Once the buffer fills.. then you see the drop in speed down to, my guess would be, 10Mbit/s or less.. Seeing how the test file is less than the buffer on the WRT54g, i am running DD-WRT, you would see higher speeds because you are pulling to the router faster.. As far as the TMN server knows your router is the device making the request. So once all of the traffic has been retrieved, the test is over. I am going to bet if you were to test with a larger test you wouldn't see more than the hub speed.