Generally they do.. my bosses MyGica and Nvidia shield allow updates.
Weither they continually do updates, is another whole story. They may get to a point as they get older, that the provider may not longer push OTA updates for them.
You can sometimes push custom rom updates to them (but run into bigger issues of it not possibly working properly with the hardware)
Rogers 9865, LG 47LV5400 LED TV, Onkyo HT-R690.