Correct me if I'm wrong, but Revolv isn't working with an API. They're basically hoping that Hue, Nest, and the others, don't break their product. It's a bit of a crap shoot.
Hue published their API and I believe nest finally did too (or at least they are working with partners on an API). I don't believe this is all reverse-engineered stuff.
Published API can be deprecated or abandoned.
...which then upsets your customers. What's your point there?
Even a published and currently supported API is only as reliable as the company(s) providing it. Which is nothing new, of course.
It is unclear where or how a decent set of reasonably long-term interoperable standards will evolve in this space. The long term part is hard since home automation equipment tends to be adopted and used over many years.
That X-10 is still around could be viewed as testament to how slowly the wider consumer home automation space moves.
Perhaps Google + Nest will surprise me and create something durable that can outlast Google's direct interest and support.