They can revoke access for clients that don't comply with the display guidelines. They probably don't want to be in the business of policing 3rd parties like that, but they have the power if they want to use it.
Yes. Additionally, blocking access past 100k also stops one client from being the-tail-that-wags-the-dog too. Imagine a dispute where Twitter faced blocking the chosen mode of access to a significant percentage of users, or caving to the client owner.
