They gather other facets of your personal life...ie your "information" dipshit.
Again...who cares. Listen to my phone calls they are pretty boring.
The obvious difference, which you miss, is that I choose to use those services and agree to the terms those companies ask, I can also choose not to participate. It's my choice. The government, which the NSA falls under, has to follow the constitution, it's not my personal choice to have my entire digital life recorded and stored.