Other systems should "learn" from it, sure. It is hard to change Maxima, unfortunately, since it's entrenched in its roots from the 1960s. That's no excuse for making it difficult to use.
I think Sage's Python interface is doing better and better, learning what it needs to learn from Mathematica, including its documentation and interface.
I definitely don't agree with you that everyone should use or learn Mathematica though to learn it. As a student of computer algebra, I'd have to contend that Mathematica actually does computer algebra remotely correctly. A much more beautiful system for doing computer algebra was Axiom [0].
