Well, I learned a few thing by browsing the AV forums, while waiting for 50b550, that influenced my decision to drop the samsung and rather go for the Panasonic. I same sharing these in case they could help others as well.
1. Beyond a viewing distance of 5 feet, the difference b/w the PQ of a Full HD vs HD Ready TV is not discernible. My viewing distance is 12 feet. So, Full HD vs HD Ready was no longer a factor for me.
2. Panasonic is extremely resistant to Image Retention and burn-in whereas samsung is prone to this issue. I was concerned because the channel logos plus the tata sky logo is always on. Also, I found reviews about 50b450 where users were complaining of screen burn in. This was the major factor that influenced by decision of not to go for Samsung.
3. HD Ready is better than Full HD for SD viewing. And Panasonic plasmas are much superior to any other brand/Samsung in displaying SD. So, it made more sense to go for a HD ready display from Panasonic. I even found reviews where users suggested that for SD Panasonic was better and for HD Samsung was better. I knew I would be viewing SD 80% of the time so I decided on Panasonic. Also, I have now watched a few HD movies on my Panny and they too look great. I guess HD would look great on any HDTV, unless we are critically analyzing that, which is anyways beyond me.
4. I got a 3 year warranty as part of Diwali promotion on panasonic which gives me real peace of mind.
The above factors led me to drop the samsung, even though it was available in GIP, and rather go for Panasonic.
I gathered all this by reading reviews, going through AV forums etc. so this might not be accurate. You can do your own validation by googling on the info. Overall, I am very satisfied with my purchase.