its mostly because of copyright reasons, in japan the copyright is more strict than here in US and they would have to pay a lot for playing someone else songs.
Unless there's other people in the family/friends into anime or fripSide, they are perfectly safe, unless of course, youtube pulls it's weird tricks and shows this in relevant videos. Just like how people get from Halo/Skyrim/CoD to the "weird side" of youtube.
I always thought the reason cover the face was this reason pointed out by member186 Or because they Couldn't until he/she was 18, Or they just got used to not showing their face when making a video. Or.. They want us to focus on how they play it instead of their beautiful face..
BTW I am Korean, but I have been to Japan once, and know MANY people who make youtube and nico videos from AND who lived in Japan their whole life and they tell me its only because they are shy and that there really is no law about hiding their faces unless they are celebs such as actors, boy bands, etc :P
