The Australian examples are very odd - the pictures of our general purpose outlets are normal (figures 1 and 3 when you click on Australia), but most of the rest is unusual and either fairly or very rare.
For example the plug shown on the main page is very non-typical - it's a re-wireable one which you very rarely see (because it's generally only if a plug has been damaged and had to be replaced) - almost all the plugs normal people will ever use in Australia will actually be fully moulded.
Secondly it's right-angle, which is not incredibly rare but not the default - normally you'd only see that on some power-boards (what the US I think calls 'power strips') or some extension cables. Appliances usually have straight plugs, the right angle one you do see on them sometimes but not as much (maybe 5-10%).
When you click in to the Australia page, the back side of the plug is also shown as piggy-back which is also quite rare (usually only on extension cords - such as in figure 10, that one is fairly normal).
Figures 5, 6, 7 and 8 and 9 are also things you'll almost never see (it does say in the case of figure 9 that a rewirable piggy-back as shown is now disallowed by our wiring standards).
Some of the example pictures would be better to be changed to something more normal, and the detailed page could probably be broken up into typical, specialist and rare/obsolete sections because it's confusing having it all together.
They used to be more common in the pre power board age (piggy backs, and screw terminal - they were very common back in the day), I can't see a date anywhere on the page. 5-8 are more specialist.
It's an interesting point of view, conversely, as an Australian of some decades, they all look fairly normal to me and a subset of a greater spectrum I'm also familiar with.
Right angle plugs may well be less common (in your experience) but they're essential for, say, getting power from the wall to a breakout strip (for TV + games consoles, NAS, media box, etc. corners) when the wall plug is behind a low cabinet / cupboard.
In any case it's a museum, a catalog, intended to show a range of things that do exist, even if a good number may not encounter them frequently.