Found a Task manager that actually makes the X button on the bottom close apps instead of minimizing in WM 6.5.1, all edits of setting have to be done through the registry but the post has the info for all the registry keys....
The post says it closes by default however when I installed it when I taped X it only minimized, had to go into registry to change but after that it has worked like a dream!
http://forum.xda-developers.com/show...5&postcount=63
Hope it helps