Four card majors and weak notrump?

Twenty years ago, four card majors and a 12-14 notrump dominated bridge in the British Commonwealth. If a serious partnership in New Zealand played five card majors and a strong notrump, you'd look at their card and say "Oh yeah, my grandmother used to play that. Do you play Fishbein as well?".

That's not the case any more. In New Zealand and the UK, top pairs are switching to Standard American or 2/1. The Australians have always been a bit closer to the American style, but the weak notrump is losing ground there too. What has changed people's minds?

The obvious reason is that the most successful pairs in World Championships use these methods. But there are some equally obvious objections to this:

1. If copying World Championship winners is so clearly right, why aren't we all playing Blue Club?
2. The USA was winning for a long time before we started copying them.
3. The Americans have markedly superior card play. If Bridge had no bidding and was scored on play alone, I expect the USA would have won even more World Championships.
4. I'm not entirely sure that the weak notrump has done badly in World Championships, when considered in proportion to the number of players using it.

If we just consider four vs five card majors and 12-14 vs 15-17 NT, I think it's nearly impossible to establish objectively which is best. My gut feeling is about a 60-40 preference for five rather than four card majors and a 75-25 preference for weak rather than strong notrump.

Switching to five card majors may be explained by a desire to use the Law of Total Tricks and Bergen Raises. I think this is an error, for reasons which are spelt out clearly here. However, there's no reason that five card majors and strong notrump need to necessarily go together. If people are switching to a strong notrump for that reason, I'm fairly sure they are just mistaken.

I'll post a detailed explanation of my preference for the weak notrump later.