Secondary cable TV boxes with built in 4 port 1GB ethernet ports
The google fiber tv box uses MoCA 2 (I am pretty sure it is 2.0) in any case it has a 400/800 (bonded) mode so if a Gigabit port was provided it would be artificial (device would connect at 1gb) but the max through put with the MoCA spec is 800. considering the Google TV box would be doing traffic shaping you would probably be back to the 400-500mb range (better than 100mb) but the box would need to do more advanced functions to ensure TV quality.
By putting only a 100mb port on it the box can be a "dumb" MoCA adapter.
Rick Hornsby commented
@Robert Despite having a 1Gb ethernet port, the RG-6 <-> ethernet bridge in the Gen 1 box limited the practical top speed to around 130-140Mb/s. If you tried to sustain a data transfer at that rate for more than a few seconds, the physical components would get hot, forcing the TV box's internal fan to come on to cool it off. It made quite a bit of racket.
In the v2 boxes, they removed the fan (noise?), meaning there was not enough cooling for the 1Gb hardware, so they dropped it down to a 100Mb port.
I don't think it was because of the RG-6 (although that has limits as well), but rather because of the bridge and the noise the fan made. By giving up just ~30Mb/s, and limiting it to 100Mb, the fan could be removed keeping the noise down, and reduce the TV box's physical footprint.
Robert Killory commented
It is not necessary to have 4 ports as long as the 1 port is Gig. If you need more ports, it is reasonable to expect you to get a switch or WiFi router for it, but to have it be 100 meg is silly. If it is because of bandwidth limits of the coax portion, say so and we will understand.