WWW
Remember a B777 still has an e-type compass and a stopwatch. Boeing wouldn't put them there without a reason.
They are there because the FAA says so. Is there a failure mode on a 777 where you would lose ALL your navigation instruments (including radios) and still have enough electrically powered stuff left working to be able to fly and land the aircraft? And if so, how likely is it to happen?
SAS
IO540 the reason you get instructors jumping up and down about GPS (and I'm nowhere near being grey) is that it does degrade the basic skills, just read GASIL etc. for tales of people calling D&D because their GPS has failed.
I accept GPS cannot realistically be taught in the 45-hr PPL course. Especially as the average student takes 50-60hrs already, and many schools would not have the money to fit out their planes.
I do read GASIL for what it is worth, been to the CAA safety presentations, etc. These are mostly aimed at 10hr/year pilots flying WW2-equipped aircraft - probably the majority of the fatal accident statistics which is why the CAA and D&D plug away at the same stuff everywhere they go. If your GPS packs up you immediately fall back onto VOR/DME (which you've been using all along, concurrently). If you get a total electrical failure then you can't call 121.50 either, so you've got to carry a handheld radio, otherwise you better hope to either be in VMC or be able to descend into VMC above the MSA. I carry a handheld GPS and a handheld radio - as well as having all the stuff in the plane.
As regards ex-GPS D&D "customers", there will always be people getting lost doing heading/time/map navigation, getting lost wrongly doing VOR/DME, getting lost wrongly using a GPS. The only difference is that the first category is "OK" because they were doing it "the right way". There is no solution to the first one, other than many hours of practice and currency, and of course good visibility. The other 2 are usually silly procedural errors (flying 80 instead of 180 or creating duff user waypoints on a cheap GPS) which are easy to avoid if you use both systems.
None of this is rocket science.
Most instructors will always dislike GPS because of the above reasons, but it is a huge backward step to insist it should not be used afterwards.