Those expensive cables will only yield a difference if you have the best of everything. If there is nothing else you can do to make your entertainment system better, then you get the best cables. Otherwise, there is no point to the expensive ones.
agreed, unless you have an extremely high end projector or TV you won't be able to tell the difference much unless you play alot of high graphic games, then you can notice very small pixelation if you know what to look for