But this is how I receive all subsequent beta of iOS 9 before installing iOS 10. I don't have profile being installed.Not true. If you remove the profile you will not see future updates OTA. Profile is required. El Cap is different. Once you install a beta, the App Store sees you running beta software and gives you subsequent updates.
If you don't trust me, just delete iOS 10 beta profile and see if you still can receive iOS 10 beta 3. If you can, I am right. If you cannot, you Are right.