That's an incredibly ignorant and inflammatory thing to say.
Hell, it was always true. The point of a diamond on the engagement ring was because it was assumed that you had kicked the tires on that part of the relationship, and the engagement fell through, then that woman had something she could sell as a nest egg for her new life as a forever alone spinster, being the 'broken woman' that she was.
As far as diamond engagement rings are concerned, it's about a century old tradition at this point, so four or five generations. That's a pretty long time for the purposes of this discussion.
And this comes form someone who didn't get their fiancée a diamond ring for various reasons.
I should also have said this was more a side comment. I don't think it detracted from the overall point made earlier.
These days, pretty much the only people who never have sex before marriage are religious extremists. Those people also tend to believe that you can be tortured for eternity if you get a divorce, which probably reduces the incidence somewhat.