The browser never takes you to a different app and there is a forward button as well if you don't like where it takes you. I'm not saying that iOS task switching is good, I'm just saying there is a reason that there is no global back button. I expect that Apple will make changes to task switching one way or another eventually but it's not going to be with a back button.
That's a nitpicky distinction based on the meaning of "app". The back browser certainly can switch you between applications. A user will be equally "confused" by their screen switching from facebook to gmail as they will if it switched to the photo app or whatever.
I'm just saying there is a reason that there is no global back button
Because as part of the original design, iOS had no particular place to go back to other than the home screen...hence the singular home button...which actually is a global back button of sorts.