Interesting. I had modified asix.c to include the Apple USB Ethernet adapter IDs, and it worked fine with firmware 1.6 (except it dropped out at random hourly intervals, and needed a restart to reconnect.).
asix is the Linksys style device, and pegasus is the Belkin style device I believe. Maybe Apple's changed the internal hardware in the newer adapters?
My Apple USB Ethernet adapter is model A1277, EMC 2147.
EDIT: It doesn't work out of the box though with firmware 1.7. I'm looking at recompiling it at the moment, using the 1.6 kernel source (as it doesn't seem like the 1.7 kernel source has been released yet).
EDIT #2: I have recompiled the asix module with the changes I made previously, and it works on firmware 1.7, with the same random drop out issue unfortunately. I looked around for newer revisions of the source file (without downloading every release and extracting the source), but the ones I found were too new (required a newer kernel version due to socket buffer changes).