Swh,
Thank you. Perhaps you could enlighten us about what percentage of RNAV routes have LSALTs published?
Blip,
That "bright spark" probably has saved industry many many thousands of dollars by deciding that RNAV routes don't require LSALTs. And his justification probably was, as you hypothesise, that most RNAV routes are flown by higher-flying aircraft.
Another consideration here is that Grid MSAs provide a higher level of safety: instead of the highest LSALT for the whole segment, they allow you to descend (if that's what your worried about) to the lowest altitude for the grid square you are in at the time, that being far better than being "stuck" at 8700ft for the whole segment. You will, of course, know what grid square you are in becuase you are on an RNAV route and your therefore would be navigating with an appproved RNAV system...
There are hundreds of "required" RNAV routings that don't have LSALTs published