Mystic, yes I have seen many photos of those UK 45s that are made for a standard spindle, but can be punched out for 38mm. Never saw one in person, however!
I guess I should have done the Google thing before asking my question here - but I know there are some industry members here, so that's why I asked here first.
But I did just Google styrene records, and I think I got my answer. I gather that styrene itself is a less expensive material. (Higher record company profits.) And the stampers that are used for styrene injection molding are not subjected to the "harsh" conditions used to press vinyl - so they last longer. (Higher record company profits.) And used styrene can be recycled with better results compared to vinyl. (Higher record company profits.)
Stampers for vinyl must undergo heavy pressing force (in the tons), and must continually be heated and cooled. But styrene is injected as a thick liquid, there is no pressing operation, and this is easier on the stampers.
So, once again it's the bottom line, profits, that is the reason styrene was used at all. From what I read, nearly everyone feels styrene is inferior (breaks easily, lousy glued-on labels, more prone to wear). I also read that styrene was not widely used in the UK, as it was here in the States.
You can check out this link: