As I wrote, but to make it a little bit more explicit, the centerpoint moved as you panned. The vectorial stream was performed directly in WGS84. This allows t

As I wrote, but to make it a little bit more explicit, the centerpoint moved as you panned. The vectorial stream was performed directly in WGS84. This allows to have of a country like Germany in view with very little distortion. As the zoom progressed outwards, it would morph to mercator. Nobody really noticed (sadly), and the choice of falling back to mercator was also due to it's popularity making it sort of "expected" more than anything else. The key point is that the reprojection was dynamic, and done on the client, optimized for the current viewing conditions. Stuff that today you can perform via JS without any problem if you forego the idea that maps need to be pre-rendered.