I think you are quite right. It appears that has been going on for some time.
I have an Nuvi 855 unit that has more features an add-on capability than the newer units.
The 855 has an Mp3 player, talking book capability, FM transmitter, language translation capability.
I can connect an external antenna, an audio out to connect to the aux in of my radio.
The battery even easily replaces via a slide open panel on the back.
I question the value Garmin is offering these days.