Not entirely accurate (Score 1)

Whether are not there are few major game titles built *entirely* with free/open source software, there is quite a bit of it going into parts of game engines. Case in point: we have been building our commerical game engine for some time now using several free/open source software components:

SDL (http://www.libsdl.org)
GLEW (http://glew.sourceforge.net)
ligpng (http://www.libpng.org)

The game servers themselves are running on all free/open source software:

FreeBSD (http://www.freebsd.org)
Apache (http://www.apache.org)
ACE (http://www.cs.wustl.edu/~schmidt/ACE.html)
TAO (http://www.cs.wustl.edu/~schmidt/TAO.html)

Likewise we have been building the engine using free/open source software tools on free/open source software operating systems:

GCC (http://gcc.gnu.org)
GNU Make (http://www.gnu.org/software/make)
Bash (http://www.gnu.org/software/bash)
GDB (http://www.gnu.org/software/gdb)
DDD (http://www.gnu.org/software/ddd)
Gentoo Linux (http://www.gentoo.org)
MinGW & MSYS (http://www.mingw.org)

Finally, we are planning to release much of our own software infrastructure as free/open source software. Thus saying that the open source development model does not make sense for game development is not entirely accurate.

Arc