*sigh*
http://financialsoft.about.com/od/softwaretitle1/f/upgradevupdate.htm
2.640 is no patch, but an
upgrade. It comes as complete, new installation in itself (old installation needs to get deinstalled), and introduces plenty of totally new stuff and features, and adds several new platforms as well as new wireframe models and highres textures replacing already existing platforms, it also replaces parts of the existing engine, improves the sound suite, and replaces old infantry bitmaps with animated 3D models. It includes also plenty of bug-fixing.
It will receive a
patch fixing some bugs and unrealistic values later this year - for free.
An upgrade can
include patching, but goes beyond that. But a patch never is an upgrade.