And there's no way to tell if you're at the first "point" of the current application(in which case it will switch you to the previous one), or if it will go back to another place within the app.

And the Android OS doesn't determine what the back button does. Individual applications do. So you're dealing with an OS control button that's extremely context sensitive and application specific. You don't know what the button's going to do until you use it in any app.

That's not really true. The vast majority of iOS apps with nested pages will have breadcrumb navigation at the top, with a big button either saying "Back" or telling you exactly where you will be going back to.

When you launch from one app into another, that's a different matter. I agree that can be annoying/confusing. But no more annoying/confusing than I've found with Android, where I've had some apps go back to the calling app and others going back up their internal chain (to what would normally be the parent screen of the one that you've landed on).