Need not be the case. Some modem + router comes with just one ethernet port as well.
As for the GoFlex Net / Pogoplug it will be the same for your purpose, so just get whichever is available for cheap. I like the Kirkwood based devices ie the Dockstar, GoFlex Net, Pogoplug v2 as it has a much newer Kernel etc.
You can get a Pogoplug P21 for about 2.9k from JR.com through ICC ShopAbroad
is this the same thing at 2.7k on GEB? - http://orders.ebay.in/ws/eBayISAPI.dll?ImportHubViewItem&itemid=170798832443
It only says media sharing device. Seller is JR.com