I agree. To narrow it down, IMO the main problem is breaking interoperability (on both sides). Web is built on open standards to ensure diverse systems can talk to each other. As long as systems comply with well defined interfaces they should be able to communicate.

A company can introduce additional constraints on top to limit access. However this should still be done based on standards. Using a variety of derived properties to block specific device type is evil in my book. My 2c.