Gomer sorry but I can't agree with your comment that non-WAAS gps is more accurate than ILS, nor that its error is 10m. The whole problem with gps is that there is no maximum error. You could say "the error is no more than 10m for 99% of the time" but what about the 1% or even 0.1% when the error is 100m or more. The maximum error for 0.001% of the time is perhaps 1000m (making these figures up but you hopefully get my gist). GPS near the ground can be further degraded by multipath reception from buildings etc. So outside of 99% of the time, WAAS makes a big difference horizontally.
RAIM gives a certain degree of protection but for a tso129 receiver the best it can do is to tell you that there is a RAIM problem and the best you can do is to discontinue the approach - not very good if you are already at your alternate on minimum fuel with no other approach aids.
FDE RAIM for tso145/6 receivers deals more gracefully with RAIM problems by deselecting the faulty satellite and, if you still have enough satellites, you can continue the approach.
ILS of course has the advantage that it gets more accurate the nearer to the ground you get. Yes ILSs can fail too but its a so much simpler and more robust system than gps that the probability is remote.
HC