sima b'PIHEM vs sim b'OZNEI Yehoshua

In our parsha we have the very last mitzvah in the Torah, "v'Atah kisvu lachem es ha'shirah ha'zos... sima b'PIHEM," to write a sefer Torah and, literally translated, to "place it in their [the people's] mouths," an allusion to Torah shebaal peh. 

This pasuk reminded me of an earlier pasuk.  After the war with Amalek Moshe is told "ksov zos zikaron ba'sefer," to write what happened in a book, "v'sim b'OZNEI Yehoshua," and, literally translated, "place it in Yehoshua's ear," also an allusion to orally transmitting Torah shebaal peh. 

Both pesukim refer to writing a book, both refer to teaching the lessons of Torah orally, so why then does the pasuk we read this week refer to placing Torah in the people's MOUTHs while Moshe is told to place Torah in Yehoshua's EAR?  

Seems to me that leaders are often good at using their mouths to give orders, but sometimes need reminding to use their ears as well, to listen and take advice and guidance from others.  The flipside is that people sometimes get good at just following orders, blind obedience, and need to be reminded that they can, and should, use their mouths to speak up and contribute their own ideas and insights, not just act as automatons or yes men.