The only reason aside from "avoid the wireless" I can think of is that it might be speaking some kind of router-ese that wouldn't be going over the switches. Perhaps UPnP is like that? I don't know, I've never used it. However, I don't think it SHOULD be that--a proper network protocol design shouldn't REQUIRE something to be directly attached to a router, it's simply not feasible in many circumstances.
As far as the GigE goes, if you're doing transfers over Wireless N or to GigE equipped devices of large files, upgrade. If you're just streaming stuff, don't. Remember that the pipe coming into your house is smaller than the pipes IN your house, and if you're only streaming online or playing music, you don't need GigE.
