My point is that right now I buy a failsafe Rx of true 9 channels (not 8+1 like Futaba) for £60 which I can still use if sometime in the future I buy a Tx of a totally different brand. If I buy a PCM Rx it will cost me £100+ and can not be used if I change my brand of Tx in the future.

Outside North America all brands of radio work together, the shift incompatibility doesn't exist for us, so we can be quite mercenary about buying the Tx that suits us best and not have to worry about the added cost of changing all the rx as well, unless we have bought PCM rx in which case we do tend to get locked into that brand. Using PPM failsafe gives us back the total freedom to upgrade our Tx to whatever we want and not feel locked into JR or Futaba or Hitec or Multiplex tx because of the cost of replacing all the rx.