If you buy the LNT 4053 at Amazon, there is no tax or shipping, so it would probably come out nearly the same as buying locally for you. The Wal Mart tv you show will be missing elements and probably quality from the 4053. I got mine at Amazon and they are good and reputable, even have a 30 day return/price match policy. I find Samsungs do as good a job as any on SD upconversion.
I posted the following at another forum when asked the question about SD, so I'm posting it here in case you want more info about that aspect of these tvs:
SD TV is a real mixed bag. Some things I have found:
1. If you get an HD cable box and watch SD tv on their HD tier of channels, the reception is almost always excellent. I use component cables with FIOS TV and find the SD looks almost as good as HD on this tier, only in a 4:3 aspect. If you plan to stretch the SD signal to fit the tv, you will loose picture quality and the people will look fat. Plasma may require you to do this to avoid burn in lines on the screen. Something to think about.
2. The SD channels on the plain digital tier can be good or not so good, depending on the quality of the particular channel's signal and quality of original filming/taping.
3. SD channels received from a non HD cable box are not good due to limitations of the type of cables you can use, generally no component output is available on these boxes.
4. The provider you subscribe to can compress signals so much that SD and even HD reception can suffer.
So, if you have an excellent provider who does not compress the signal, use an HD box and stay in the HD tier, it all looks great.
Otherwise, the above is what I have found.