Faster mobile data via 3G WiFi router than 3G USB modem?

I have a Cradlepoint PHS300 and noticed something interesting when using mobile data: if I plug my 3G Sierra  Wireless USB modem to the PHS300 and connect my laptop to the router via WiFi I get faster speedtest results than if I plug the 3G USB modem directly to my laptop.

This is obviously for the same network, same location (Auckland CBD), around the same time (as in plug to laptop, test, plug to PHS300, text, plug back to laptop, test)...
Also the connection seems to be more reliable.

Interesting. I know both the laptop USB adapter and the 3G USB modem are USB 2.0, but why the speed difference?

And no, it's not a paid advertising for Cradlepoint products, but I would be interested to know if anyone have similar experiences with other 3G/WiFi routers.