Different places and states have different rates of sales tax, local tax, octroi, etc. Add to that, places like Delhi and metros are where dealers can sell more units and hence can sacrifice a bit of commission because the inventory turns are faster and hence lower cost of carrying. In smaller towns, there are not many who will end up buying a 100k worth of TV. The dealer has large carrying cost and hence will not be agreeing to more discount.
One can definitely get it from a dealer in another city at a lower cost. Ahemedabad is a good example as Mehsana is only some 70 km north. But then there is cost of transportantion and local dealer support.
As regards to the various prices mentioned, I have not seen any 50ST50 sold below 1L. Various threads/posts have mentioned prices but no firm sale - perhaps mainly because of no stocks. Correct me, if I am wrong.
Is the 50GT50 worth for 116K? Yes and no.
Yes because ... GT50 is THX certified and produces twice as many shades of grey than ST50. The set has higher dynamic contrast ratio which "should" mean higher native contrast too. This means blacks will be deeper, more shadow details. THX mode means ideally suited for movies. Less callibration, etc. It has extra HDMI and USB port. It has face recognizing 2D to 3D conversion. The set is also visually more appealing and thinner panel. THX alone will be adding to 2~3k of royalty fee to the base manufacturing cost (and making George Lucas richer). In short, if one is watching pure 1080p stuff, high performance will be delivered.
No because ... all the magic and betterments will be felt only when fed with high quality picture source. If one is watching DTH with SD and some HD, downloaded content, all the extras will not play much part.