There is no explicit foolproof assurance from either Apple or Google, but in Apple's case they haven't been known for introducing products and then dropping all support for it when it fails to live up to sales/strategic expectations.
In fact Apple's modern track record is pretty impressive - the latest iOS runs on a phone introduced in 2011.
Google's "throw everything at the wall and keep the stuff that sticks" approach is IMO one that only makes sense when you discount brand value completely and assume nobody will remember the stuff that didn't stick, and their unceremonial shutdowns. It's a theoretically appealing approach but IMO impractical because people remember.
Even when Google compensates people for the shutdowns - see the Nexus Q - it still leaves a bad taste, and makes people wonder if they're buying a real honest product in a particular space or an experiment to be cut lose at a moment's notice.