It's not that much of a myth. When Google first announced that the Galaxy Nexus was not getting KitKat, I was pretty disappointed, as I had one too. I looked into why there was no official support, and when I found out it had to do with the firmware, my gut reaction was "WTF, that makes no sense." Digging some more, I found out that it actually has to do with kernel driver-firmware compatibility. Google wanted to ship an update, but they needed changes that TI was no longer willing/capable of making. In order to release KitKat on the Galaxy Nexus would either require Google to reverse engineer the hardware and make their own radio firmware (not likely) or holding back the kernel to the same one on 4.3 (subpar experience if it even works).

Neither the Glass nor Moto 360 suffer from this problem since neither has a cellular radio.