Eh, that sounds like good advice to me. I shower whenever I get smelly, which sometimes can be every two days if I haven't been very physically active. In the US/UK, people usually take a morning shower, while I prefer mine in the evening.

Just because a culture is different doesn't mean it makes no sense.

Well, barring actual dirt on your face, if you don't smell no-one will be able to tell how often you shower. Or care.

Yep, that's exactly the rationale. Some people shower just-in-case, some don't. Different strokes.

No, it's not the standard world wide. For the simple reason that consuming that much water and energy (to heat the water) costs a lot of money. And most people in the world don't have that much money.

In some places (e.g. Central America) they do use cold water to shower. Might be hard in cold climates though.

The implication was not. I can really only speak for the UK/US, barring anecdotes I hear about the Paris Metro.