Pipe dream, but I really wish we would make it illegal to use the terms "Buy" or "Own" for digital goods that can at some point not exist outside of your control.
I give you a dollar and get a DRM-free video file? That is buying.
I give you a dollar and can watch a video file an unlimited number of times in your app? That is not buying, and it should be fraud to claim that it is.
Having some word or phrase marking the end of a request makes the voice recognition a little more reliable. It doesn't have to be polite, but being polite when it's totally unnecessary is a good habit to build.
"Do X please" makes it unambiguously clear (to a machine) where the end of the request is, whereas "Please do X" is mostly pointless.