@Shagpile - iOS is now multi-threaded, one of the main benefits being the ability to process in the background. Processing = clock cycles = power.
Apps in the background definitely access Location Services. One example of this is Find My Phone, which always runs in the background and can be used to find lost phones even when the app is in the background and the screen is locked.
A lot of apps use Location Services even when they don't really need to or are unimportant, like Facebook, FourSquare and Camera.
ARM processors are optimised for low-power, but are expected to do a lot of work with small batteries. It's important to be economical with processor load.