Alright....time for non-gamer marketing perspective:
Having a mic built into the rev remote would be perfectly natural, and it would coincide with Nintendo's mission for the Revolution...getting more Non-gamers involved in gaming/interactive entertainment. Nintendo already took the step to make the controller for the Revoltuion look more like a TV remote to appeal to those who might be afraid of tradional controllers. Why not make the rev remote second as a traditional handheld microphone, as well? Can you say NON-GAMES. For example, the Revolution might have title like..."Kareoke Extravaganza" (older, tradionally non-gamer audiences would like that), "American Idol" type game (voice and motion can be captured), Game Show / Trivia (ie. Jepordy) type games (where many players buzz in and speak into their rev remote Mic to answer the question), Brain Training / learn new foreign language / academic non-games, Voice activated search engine to go along with Opa Internet Browser, Voice chat of course, Voice recognition messaging/ email, Vocal minigames like who can scream the loudest or who can read the passage on the screen the fastest and most accurate. Holy crap...Nintendo should be stealing every idea I listed here if they haven't already. Either that or I should be working for Nintendo.