[surferbayarea]

Well the reason FB/Foursquare/Google etc add these to 3rd party apps is so they can get data. Example if you visit a website which has a Facebook like button, your browser fetches the js files/which maybe even makes an API call to let FB know your IP (and hence location). All this data is fed to the giant system that feeds you ads. Adding their SDK to other apps/sites (even if there is no user facing need) is a common strategy used by most big companies to get data. In return the app that puts in the SDK gets $ from the company.

[traek]

Of the companies you named, Foursquare's business model explicitly revolves around paying apps for user location data and selling it.

I doubt (and at least from my experience around SV, haven't seen) that FB/Google are paying apps to include their SDKs.

[lucasar]

You have no idea what you're talking about. Apps use the Facebook library because a good portion of end-users want to be able to login with a Facebook button --or Google, or whatever that doesn't require them to create a user/password account. It's just that simple.

[surferbayarea]

I have been witness to such business partnerships to embed SDKs to siphon telemetry/other data. The world is not as simple as you think...

[MCKapur]

well, this would be extremely believable

[ratww]

If you only need login, then you can have the same functionality without the Facebook SDK or Google SDK by using OAuth.