That's a valid fear, my old Samsung had an issue where it would always stretch any screen to the full width, no matter what the settings were. Happily my new one is better in this way, and I assume it's related to its TV pedigree (necessity of handling 4:3 broadcasts).
Think that, if it gives you comfort.
While I do realise that the concept of gaming on a TV is abhorrent to a lot of PC gamers, they do roll of the same assembly line, generally. The Samsung model I use starts out as a tv with digital cable and terrestrial tuners and audio, and strips out features until it reaches the model I have, dvi-d+hdcp.