It's hard to tell what kind of juddering you are seeing. It could be that the tv is just bigger than you are used to.
If you were watching a blu ray or vudu, the movie would be in 24hz and I think the LG would do 60hz in that case which might introduce some juddering. However this is what you would get from any regular DVD and from most new and old TVs, except some high end models.
I just watched the hurt locker myself on a 58" with proper 24p handling, and it was kind of difficult to watch at some points. It has some very uneven handheld camera work.
Most of the things your salesman said sound like BS.