I agree, seems like a minor thing sometimes to say please and thankyou but I was also taught the basic manners by my parents, including not to stare at people.
I also am sure to say thank you on the way out the door of the airplane to pilot and copilot who are usually standing there along with any other FA's whether they were serving in my cabin or not. I once profusely thanked a pilot who made 2 attempts into Orlando in very bad windshear (he told us as he dove in). He had to turn back to Tampa. Needless to say I thanked him profusely that we went back to Tampa - what scarey few moments!!