It was added because way way back then, unlimited data plans didn't yet exist (in the US) so wifi was almost always preferred by apps (even hard-coded into early versions of Android Market/Play Store, forcing wifi to be used to download certain apps over a specific size) over mobile data. In earlier versions of those apps and devices, you'd often get pop-up warnings when using mobile data that it might incur data overage charges. Those were quite expensive so I understand why it's there. But it's not 2010 anymore, and Google, while not relying as much on wifi, haven't removed that code in the source.
Heck, I remember when texts were charged by the letter (SMS on then-Cingular Wireless circa 1997) and if you ever wondered where 'txt sp3k' came from, that is it. Saving letters by abbreviating them saved $$$ to send a message. A simple 'r u thr?' was a nickel and penny, while 'Hello, are you there?' was 18 cents.