Noticed this all over this bit of Poland... guess they paint out the ceiling and wall junction in white, then masking tape the top 30mm of wall before painting.

Seen it with paint and wallpaper but not tiles. 

In this picture only the wall with the frame has any colour (kinda greeny lime) the other walls and ceiling are white.

Good way or what?

I like that, and I can see the logic. It would also hide an imperfect wall to ceiling joint.  I will have to suggest it when we get to decorating.

 

I wonder how it would look if you also did the same at the corner?

 

I have painted walls "Polish style" at home and I think it looks very nice, I certainly would not change it

Is the origin of "polish style" an attempt to create the illusion of coving without the material expense? Whatever, I like it.

Sometimes people use this method, when have curves walls. But a lot of people use becouse it is aesthetic. Maybe it is illusion of coving.