US doesnt replace them with raptors because the Raptor cost is too much for the AF to handle with current threats to budget cuts. The whole of US military is slimming to keep the cost low.I request all to keep unrelated things out of this thread as it will invite a troll fest ...
A correction " Various sources say that induction of LCA will only be possible after 2015 when it gets FOC " ... I will happy to post links if you want but the news was very well reported here ... So 15 Months time table just isn't true , you are planning to replace Bisons with MKI's and Rafales ... Think again , are you replacing them or merely trying to get close to the sanctioned strength of 39.5 squadrons the numbers that your planners think are necessary to maintain air superiority over adversaries ? ... Different aircrafts have different roles ... Why doesn't US replace all of A10's with Raptor ?
While in case of IAF they are not worried about money rather getting the aircraft and replacing the older ones. The MKI and Rafale are the main replacement for the older MIG and SUs. While the LCA acts as a gap filling plane and to help develop the local industry.