Digital locals will have most content broadcast in 4:3 format, leaving the grey lines on the sides like that.
You should be able to "stretch" or expand, zoom, etc these channels to fill the screen by using the "ratio" button on the remote.
I have yet to read the manual on the HTL-HD, but I remember my box at school uses 1080i for HD broadcasts and then uses 480p for regular broadcasts. I think one of the format options will autodetect the signal and change to either 1080i or 480p based on the channel. This works well, as i think lots of SD programming looks better in 480p than being upconverted to 1080i.
Any OTA broadcasts in HD will not show the lines but will most likley be broadcast in the 16:9 format filling up the screen. It is just a matter of time before more and more things are broadcast in HD on OTA digital channels in 16:9 format.
You will see it when you go from a NON-HD channel to a HD channel, the format on the box will change and the screen will kind of flicker and show a strange spectrom when it switches.
I will look through the manual later on and see which format does that autodetect thing, you may beat me to it though!