Most non tech savvy people don't even have that much data to backup: most of their heavy stuff (music, pictures, etc), are now attached to an online service. P

Most non tech savvy people don't even have that much data to backup: most of their heavy stuff (music, pictures, etc), are now attached to an online service. Plus you only do it once. Differential backup would take down the size of the next backups to a few Gb, or even Mb.