Well yes there should be.. The quality of the three line comb filters they are using has gotten bad on many HDTV's though in recent years. So just because it has a 3 line filter does not mean it will be good.
My 60" Philips has one of the worst 3 line comb filters I have ever seen in it. Composite video is not an option for source feeds for me anymore. Svideo is the lowest I can tolerate with it, if I were you, I would expect the same and if it happens to be decent just consider it a bonus.
"digital" by itself really tells you nothing useful about a comb filter except that all good comb filters are digital whereas all digital comb filters are not necessarily good.
"3 line comb filter" should be the minimum you should look for, but unfortunately there is still a wide difference in quality within that category.
At least you should be able to recognize dot crawl (less is better) to be able to compare different TV sets. The red and blue lines at the bottom of the screen during newscasts and sportscasts is a good place to look, also view Barney the dinosaur (not from a VHS tape).