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.