Just tilt your head a bit :)

    9 -> g
    0 -> o
    1 -> l

You don't see any similarities between "900.91" and "goo.gl" ?

There isn't one standard way to convert a latitude / longitude coordinate into a x/y coordinate for a map. Google Maps was the first to use the Spherical Mercator projection. The EPSG (?) number used to reference the Spherical Mercator was originally 900913. EPSG:3785 now refers to the Spherical Mercator too.

http://docs.openlayers.org/library/spherical_mercator.html