I should have added: Don't forget that the price of the IP logger includes unlimited free uploads to the weatherlink.com network service - this is principally what inflates its price over the USB logger. So you can eg turn your PC off at night but the uploads from the WLIP to wl.com will continue. You can then download the archive data from wl.com direct to your PC.
Even if you did interface your USB logger to the network, it wouldn't duplicate this service - you'd still need to leave your PC running 24/7.