I would say this instead, which is probably closer to the truth: "We store this information an indefinite amount of time because, well, disk space is cheap."
I'm pretty sure that canned food companies haven't stopped using it .
So I'm a software developer, in my early 30's, pretty tech-savy. It took me about 45 minutes (a long time, I think) digging around Facebook's privacy settings to properly hide everything. Not only do you have to go under "Privacy", but also "Application Settings" - would the average user know to do that? Apparently "Group" privacy settings are under applications??? Those settings are complicated And even now I can't hide 1) my friends list from the public 2) my pages from the public. So my point is it's hard to NOT share too much publicly with Facebook.
It seems that more and more mathematicians are using a new, high level language named "research student".