It _did_ evolve into something other than a web browser plugin; Adobe AIR was launched (with Flex) as a complete solution for writing cross-platform desktop applications.

By cutting Adobe AIR for Linux out as a surprise move, they did not exactly build developer confidence in their ability to provide long-term development platforms worth investing in.

Further, by claiming "commitment" in every press release while simultaneously discontinuing more and more of the platform itself, it's getting harder and harder to believe anything they say anymore.