Sheet music redux

I've long been involved with amateur theater and music performance (my boys are performing in a Schumann recital tomorrow with the rest of their piano teacher's pupils), and I grew up seeing double bass cases plastered with Musicians' Union "Keep Music Live" stickers around the place, but I always thought this was a luddite rearguard action against the tide of recorded media that began flowing about a century ago.
But this week, the news was that Rock Band  had sold 2.5 million downloaded songs for you to play along with (it comes with 58). 
Having researched this thoroughly with my boys, the fun of this game is more in the playing than the listening — the 'guitar' playing is clearly simplified, though the drumming is pretty close to reality, and the less said about my 'singing' the better.
Looking at this in the longer view, it can be seen as the return of sheet music in a new form; before recordings took over, sheet music sold for amateur performers was the dominant form. Here's Douglas Adams again:

during this century we have for the first time been dominated by non-interactive forms of entertainment: cinema, radio, recorded music and television. Before they came along all entertainment was interactive: theatre, music, sport – the performers and audience were there together, and even a respectfully silent audience exerted a powerful shaping presence on the unfolding of whatever drama they were there for. We didn’t need a special word for interactivity in the same way that we don’t (yet) need a special word for people with only one head.

I expect that history will show ‘normal’ mainstream twentieth century media to be the aberration in all this. ‘Please, miss, you mean they could only just sit there and watch? They couldn’t do anything? Didn’t everybody feel terribly isolated or alienated or ignored?’

‘Yes, child, that’s why they all went mad. Before the Restoration.’

‘What was the Restoration again, please, miss?’

‘The end of the twentieth century, child. When we started to get interactivity back.’