I'm sorry but I must correct you here. When a composer is 70+ years dead (this is different in each country) does not mean all their work instantly becomes public domain. In terms of sheet music, publishers still own the rights over their publication of the composer's work. So simply scanning in the sheet music is still violating copyright as the edition must also be in the public domain. Take Mozart's works for example. Most are now published by "Boosey & Hawkes Music Publishers" and all these editions are not public domain.
The 70+ rule applies to public performance of the composer's work.
I agree wholeheartedly with Nikolas on almost all aspects. :)
Best Regards,
MaestroX