aa73:
I can't speak for other airlines, but as of today, AA's 75/76s are about half Pegasus and half Basic (IRU/DME). However, there is a time frame - I'm not sure of the exact date - where IRU navigation will become obsolete, and everyone must transition to GPS.
Don't know where you heard that one. RNP AR of less than 0.30 or missed approach of less than 1.0 requires at least one IRU.