That has nothing to do with Ubuntu: run xev, press windows/command keys, see output. By default xorg binds the keys to Super_{L,R}.
Besides, Open any terminal emulator and Alt/Option either behaves as Meta by default or has the option to do so, e.g. Terminal.app).
For all current practical purposes and in most default cases Alt behaves as either Alt or Meta depending on the context and Super as Super. Even emacs folks (maybe the biggest piece of software in use today relying the most heavily on Meta) agree on that [0].
Meta really does not exist anymore and all mappings one can come up with (whether they are using Alt or Super) are merely fallbacks.
Besides, Open any terminal emulator and Alt/Option either behaves as Meta by default or has the option to do so, e.g. Terminal.app).
For all current practical purposes and in most default cases Alt behaves as either Alt or Meta depending on the context and Super as Super. Even emacs folks (maybe the biggest piece of software in use today relying the most heavily on Meta) agree on that [0].
Meta really does not exist anymore and all mappings one can come up with (whether they are using Alt or Super) are merely fallbacks.
[0] http://www.emacswiki.org/emacs/MetaKeyProblems