Don't know why the command-tab thing is not used more.
I believe the keys you can assign must be different than the ones used by the OS and even most Apple apps. But all you may need to do is add another modifier key ( option, shift, control ) or two to the key you want to use. Give that a try and report back with your results, please.
There are many ( program launching ) apps that will you assign key-strokes to do the launching. I use MaxMenus but find it just as easy to select one from the menu as trying to remember what key-stroke I might apply...
But key-stroke commands are often over-looked and little used by many Mac users, IMHO.
Speaking of Command+Tab, using this keys, you need to open any applications first... like if your Appleworks, Firefox, Quickens are opened, and when one of your applications is front of you, and you want to switch to other application, you just press Command (or Apple) key and Tab... then hold Command and tab till you pick the application to bring up front of you.