What a load of old cods. There is a SIGNIFICANT difference between RNP approaches and the standard GNSS approaches. For a start, RNP doesn't have any real significance down to a value of 0.3 as this is the final approach tolerance for a standard GNSS non-precision approach. Below 0.3, RNP has a very definite significance and requires aircraft to be specially certiificated by type.
Some people might be interested to know that there are TWO very well known RNP approaches in different parts of the world. One in Alaska and the other in New Zealand. Both are suitable for B738 that are operated by specific airlines and are not available to other airlines who cannot meet the required certification standards.
For those who "push a button" to fly an RNAV (GNSS) approach with a pseudo glideslope, I hope that your system does not bust the MDA. There is a difference is you're flying an RNAV (RNP) approach, but you'll only know about that if your airline is certified for it - and if they've certified YOU for it.