Anthony,

I really don't have the time or energy to get into a drawn out OT debate.

There's nothing at all in common between the innards of a Pronto and the innards of an X-10 RF remote.

In the USA, X-10 uses 310MHz RF for wireless control of lights & appliances and for wireless security systems. They use 418MHz for their Powermid RF extenders (as do several other manufacturers). I think they picked this because it wasn't much used while the range from 300-320MHz is heavily used. Philips probably decided to use it for much the same reason.

There are off-the-shelf RF transmitter and receiver modules available from several manufacturers in 315MHz, 418MHz and 433.92MHz and a few other frequencies.

X-10 USA has used 310MHz since, at least, 1986 and 418MHz since, at least, 1992. You can verify this by going to the FCC ID Number Search page and using B4S which is X-10's FCC Grantee Code. I suggest checking only granted applications and set it to show 99 entries at a time (X-10 USA has been prolific).

In the UK, X-10 did use 418MHz for everything (lights, appliances, security) but changed to 433.92MHz about 2 years ago which is when they first started selling wireless devices in the rest of Europe. All of their European (and UK) RF devices now use 433.92MHz. Had the UK stayed with 418MHz, then UK buyers could use US models of the Pronto with no concerns about the RF frequency.