I can't comment on the rest of your question, but I don't think this is true. My informed guesses are:
eTrex 10/20/30/20x/30x/22x/32x: STM Teseo II
gpsmap 62: I was pretty surprised by this, but seems to use the same hardware platform as the above eTrex series, since panning and zooming is faster. My guess is that they use a SoC from the platform that has a higher clocked ARM CPU and perhaps more RAM?
gpsmap 64: MediaTek, most likely MT6628/6630 or similar
gpsmap 65: Broadcom, most likely BCM47758 or another SoC from the BCM4775x series
gpsmap 66: MediaTek, most likely MT6628/6630 or similar
But to be sure, we have to wait until someone disassembles these models ;).