Apple could setup an opt in group for data or use all their employees or...
There are more options than 1) scan everything ever said by anyone near the mic and 2) never collect anything.
They already do...
Settings -> Privacy -> Analytics
http://www.zdnet.com/article/apple-...ud-photos-emails-contacts-to-improve-siri-ai/
Never ceases to amaze me how people talk so strongly (and be so wrong) about things they don't understand.