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It doesn't eat that much battery and people use it.

Most newer cars have bluetooth built in, so why should someone have to go into settings to turn it on in order to use it right out of the box.
 
Bluetooth 4.0 is suppose to be less battery intensive so since they now ship with 4.0 they don't feel the need to disable it by default
 
Just like WiFi, it doesn't eat the battery any more. You can leave it on and you really won't notice the difference as when you have it off.

Really? My 4S's battery seems to drain noticeably quicker when WiFi is turned on but not in use. Maybe it's just me.
 
The neat part of having a GS3 with their tectiles is I leave my NFC on and tap my phone to a programmed tectile and it turns on my BT which pairs to the car and turns on my podcasts so I can listen on my drive home.

Now I wish I could do that with an iPhone and maybe I will be able to with the next model.
 
Battery life depends on so many factors with different radios on, the biggest culprit will always be signal strength, and if yours is worse than someone else's your phone will push up the power to get a better signal and drain the batter faster.
 
My wifi is always on and I don't notice a huge hit to battery life. While I don't use bluetooth, I can't see that being a big hit to battery life either.
 
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