Are you asking why TiVo did not build in an ethernet adapter? There are threads about that already, search for them. They probably found USB to be a bit cheaper and flexible. on the 2xx and 5xx units, it is USB2.0 BTW.
They do have USB etherent adapters available at the TiVo store, plus there are some wired and wireless at B&M stores.
TCD240080, 160 GB HDD.
FC3 Linux box running Galleon.
TiVo desktop on XP machine.
I can't undersatan why TiVo doesn't come with a J45 ethernet adapter! That USB 1.1 is a disgrace!
First of all, that's RJ-45. And it wouldn't be an adapter, it'd be a port, or a jack, if it were a built in RJ-45. Second, except for the very early Series2 units, those with model numbers starting with '1', the USB ports are 2.0.
When the Series2 was developed Ethernet was a more expensive option, and USB was also anticipated to be used for other things - at the time TiVo was talking about gaming, media devices, etc. Things changed over time. The USB system works, and it handles wired or WiFi. The CableCARD box is expected to have a 10/100baseT port, as well as USB for WiFi, as network performance will be more important with the larger HD files.