maybe you should do your research and you'd find that the 2 companies merged, those companies being treyarch and infinity ward, therefore the company making 5 is the same as 6. and the graphics engine for 5 is the same as 4, with improvements. plus, WWII gameplay is much more fun and requires more player skill with weapons. they're also keeping some form of ranking and improving gameplay by matching player skill kinda like halo does. and lastly, flamethrowers.
cod6 is trying to release spring 09, but will prolly be pushed back because of cod5.