At pattern altitude LOS is not very far. I know VHF doesn't skip, but atmospherics do play a part. But agreed, the radios/antennas are primarily responsible but the clarity wouldn't be there if the mike was of poor quality.
Incorrect. VHF "skips" fine under the right circumstances. Trans-Equatorial Propagation VHF contacts have been reported multiple times this month. Meaning: You transmit south from somewhere in the northern hemisphere, say near the 40th parallel, and someone near 40 South hears you. Folks are doing moonbounce with 100W and a decent antenna these days with the computers doing the "talking".
As far as how it relates to aviation, there's a lot of patchwork/quilting of the frequencies in use for distance separation of the stations, so even a nice solid tropospheric ducting event won't "bother" folks in another area too much usually. There's quite a bit of planning (known colloquially as "frequency ordination", but really it's based in both the science and art known as RF Engineering) that goes into choosing say, 132.75 as the local frequency for the TRACON in one city, and not re-using that frequency again for quite a long distance away.
Other considerations are not using receiver frequencies that are harmonics of other transmitters on the same site or even so close the antennas are in each other's "near fields", or alternatively sharing antennas and filtering appropriately to remove the unwanted transmitted frequency from being heard coming back down the feedline to that antenna, etc etc etc.
Ever notice that your Transponder and DME frequencies aren't multiples of any of your Comm frequencies generally, but that you could easily swap the two antennas with virtually no performance difference? And your Comm frequencies generally aren't multiples of your Nav frequencies? Modern aircraft with multiple transmitters on board and even more receivers are marvelously well though out systems to keep those radios from interfering with each other, for the most part.
That stuff was all figured out a long time ago by a reasonably smart systems engineer who could think both in RF terms and in failure mode terms.
(Bonus round: What is DME? It's just a transponder in reverse. The transponder is on the ground and the transmitter is in the air... You didn't know you had your own secondary RADAR system on board, did you? It's just that it's kinda "dumb" and doesn't have a rotating antenna...)
The world of RF is fun. All sorts of real world analog problems to solve, even in the digital age.
