[willtemperley]

It's an important discussion because it's abundantly clear that almost nobody on this thread has a clue what they're talking about.

Web Mercator != Mercator.

I suggest most people on this thread need to go away ask the question "What's the difference between Web Mercator and Mercator".

[Symbiote]

For most uses of web maps (navigation on foot, by bicycle or by car) the angles seem to be close enough with Web Mercator, and the map is zoomed in to a small area so there's no concern about the area.

No-one is zooming out the "Find your nearest Tesco" map to see Greenland.

[dan-robertson]

If two lines are at right angles in the ground and, say, outside the arctic/antarctic circles, what range of angles might be between them in a web Mercator projection?