I love the "physical" back button on my Galaxy S and find Android's overall back button concept really useful, regardless of the os version. I feel disoriented

I love the "physical" back button on my Galaxy S and find Android's overall back button concept really useful, regardless of the os version. I feel disoriented whenever I try to go back to where I left on an ios device, it's always app specific and non-standard. Opening another app from a notification and returning back would be quite difficult, not all apps have a specific action marking the end of an interaction, as in "sending the email" in this concept. How will I go back from editing a spreadsheet or some notification putting me right in to the middle of a game?