Rod1,
You are not getting this
I think I do. What I hoped to imply was that other aircraft do fly in all weathers. Corporate helicopters and others don't
just fly in bad weather during the week, obviously many customers / owners use them extensively at weekends.
It's quite easy to inadvertently under-estimate the number of aircraft in the air if relying on theories, hopes and lookout alone. Even the best eyesight and lookout technique in the best VMC conditions is far from infallible although some seem unwilling to believe this. One of the boffins from the Institute of Aviation Medicine used to travel around RAF bases in the 1980s and 90s giving an excellent presentation dedicated to the subject; it was sobering. Ten years of using ACAS systems (TCAS 1 and TAS in my case) has confirmed to me everything he said about the design limitations of human eyes in an aviation environment.
Electronic devices also have their limitations, so could never be used in isolation. A mandatory common system would help; it seems we aren't likely to get one in the short term, so we ought to do all else we can to educate ourselves and fly with consideration of the requirements of other airspace users.