>>I guess that it is just another case of fancy gear displaying information that really doesn't mean much.

Bingo

As far as we can see, 0dB means something different depending on the power output of the receiver, ie 0dB on a big honkin' receiver is louder than 0dB on a little wimpy receiver.

I always assumed 0dB was some kind of reference output level (implying that a more powerful receiver would have more numbers above 0dB) but apparently that is not normally the case.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8