Agreed, but some models include an Ethernet port and some do not, usually the most expensive do include one. Many do wireless though depending on the model. If so, you could just put a cheap router in AP mode near the TV.
Your other option is to attach to the network through one of their BluRay players if you have one.
If you do need an adapter, you need to buy their branded model, not just any adapter -- I've tested many and none worked other than their specific model adapter. Same with their wireless dongles.