Well, a nice 8-port metal gigabit switch will only run you about $20. True, it may be a lot harder or more expensive to do anything with port-specific VLAN tagging, but hardware support for that using something like DD-WRT is spotty anyway.

I'd also guess that the round design may play a part in that decision. It would definitely be less aesthetically pleasing to have a wagon-wheel of cables coming out of the base.