[OpenLayers-Users] confused about spherical mercator

[G. Allegri]

Hi everyone.
I'm a bit confused about spherical mercator property...

In the relative example from dev/examples, the SM is set for all the
layers, except the OSM ones. Why? I thought that both OSM and Google
use the Spherical Mercator. I think I've misunderstood it's effect,
when both Projection and DisplayProjection options are also set in the
map options...
In other words: what is reprojected relatively to what?

Thanks for any clarification...

Giovanni