Yes, and they can kick me (or any of my code) off of their property, just as I can kick them and theirs off of mine. They can refuse to accept any part of any message I send them at their wish, just as I will refuse to accept any part of any message they send me at mine.
You went there on your own free will and can leave when you want. No one is "forcing" anything on your screen.
(not saying I agree with this notion necessarily - just that your physical "property" analogy isn't very good).