The right ALT key is a special key used for entering characters in different languages. You can learn about it
here.
You are referring to AltGR, not the right Alt. AltGR is specific to the individual layout of each keyboard. And your more likely to find apps that use cntrl-alt keyboard shortcuts than Windows-key shortcuts. No one supports the Windows key and you can bet *everyone* has a windows key these days.
You are supposed to use cntrl-alt (right cntrl-alt) on keyboards that lack the AltGR key.
Other than using it to type the Euro... it doesn't seem to be used for anything with a U.S. layout.
