The GECK is a windows based application. It is PC only and is not availiable for the consoles.
Yep. Rather than a program that runs in Windows (like the game itself) the GECK is built around Windows architecture, which the PS3 and even XBox lack. This makes porting the game effectively impossible - it would instead have to be built from the ground up. Chances are neither console could run the GECK even if it could be brought over, consoles are specifically streamlined for a few specific types of programs and they lack the RAM to handle something like a complex game editor.
I know that some PS3 games get around this by allowing mods to be ported. However I'm also aware that this is pretty hit or miss on things like UT maps which are far simpler than what the GECK is capable of. Maps are contained, but Fallout 3 mods can adjust the actual gameworld so a converter would be difficult to work with. Even if the mod worked chances are it would be destabilizing.