I would say not exactly: If you have a public protocol and it's intended to run in multiple places or in a distributed manner, then even if the rest of the world stops using it, you and your users can happily chug along in your own sandbox.
If it's only used or useful in the context of a privately-owned/controlled environment... then you're in trouble, or likely to get there..
Google Reader ignored an important part of the RSS 2.0 spec, but I kept producing content that they couldn't parse, and if people used the tools that existed before GR, they didn't notice any difference, even though GR came to dominate RSS aggregators.
BTW, that's probably a reason why Twitter never could really support RSS, not because the spec didn't cover what they were doing, rather Google didn't.
If it's only used or useful in the context of a privately-owned/controlled environment... then you're in trouble, or likely to get there..