Eh, a 3D sphere with mapping is quite workable. Bing maps can click over an overly detailed globe and the 'sphereness' of it only starts to matter when you zoom out. It's only a bit of a strain because of the texturing, and it's not much of a strain at that.
It would not be crazy to have a more accurate interactive behavior instead of assuming that zooming out enough to see continents should still be flattened out.
Well, the benefit is this very discussion here, that 2D projections necessarily have distortion on zoom out..
Note that the 2D map is almost certainly already rendered into a 3D context, it's just how modern graphics are done. Rendering textures to a curved modeled surface for isn't significantly different than rendering them to a perfectly flat modeled surface.
Even better than Bing maps, if you go to Google maps, click 'layers', then click 'more' and check 'globe view', then you have a google maps that on zoom out just happens to render to sphere instead of 2D. Not the least bit more resource intensive, apples to apples with the same textures that it would have used to build the 2D map but just projected onto a sphere instead.