True HD is 1080 lines.
Many TVs sold as "HD ready" are actually only about 720 lines, and this may be your case.
Considering a "normal" film on DVD is showing at 576 lines then if you have gone HD you are probably only gaining a 150 extra lines so will not notice it.
I remember writing here on answerbank about a year ago saying this whole "HD ready" thing was a con to get us all to rush out and buy new TVs, but if those TVs were only 720 lines they were not true HD.
TRUE HD has to be either 1080i format or better still 1080p format.
But of course 1080p TVs are very expensive, so most people buy a cheaper 720p TV, thus losing out.