A. (Answering myself, after reading the full report that was just published):
The statistics refers to basically all the core GNOME modules with the full history, except old ones that are no longer part of 2.30 . Thus companies like Red-Hat and Novell (formly Ximian) have an edge here.
That said, Lanedo.com was established in 2003, Collabora - in 2005, Fluendo - in 2004 and Codethink in 2007 (not sure about Openismus and Litl). All of those companies are listed as contributing more than Canonical to GNOME in the report. Ubuntu has used GNOME from the start and focused on providing a good desktop. So I guess this on its own cannot skew the statistics that badly.