To put things in proportion, how many “total” radio failures have there been in the London TMA (or other major airports for that matter) over the last year? Excluding mis-selected frequencies, I wouldn’t have thought there have been too many!
As with the stats on engine failures in multis, I think you may be assuming independence where that is not justified.
I had an interesting one crossing from Duesseldorf to Amsterdam FIRs the other week in a light twin. On initial contact Amsterdam reported that I was carrier wave only. Naturally I switched boxes, only to find that I was carrier wave only on that box too. I went back to Langen -- no joy.
I was just about to try a different headset when I noticed the TX (or was it RX) indication on the GNS430 was continuously on when there clearly wasn't any transmission audible. So I switched off the GNS430, and all became normal again on COM2. When I powered it back up, there was no further problem with the GNS430, but it seemed to get itself into a mode where it was not only unusable but also interfered with the other box. I didn't get the handheld VHF out, so I don't know if that would have been affected too.
So I agree genuine comms failures are rare, but they are worth planning for.