You're right. That is a very large indicator of Google's public intentions for GWT.
But, there are a stream of applications/libraries that have been moved from in-house to open source community based projects. I guess the fundamental factor that will help support GWT is that there are commercial organisations doing professional GWT development (including, apparently Google itself). I think this will guarantee the medium-term life of GWT, even without Google's direct ownership/sponsorship of it.
Why may Google have dropped it from their publicised development tools? I guess it's because its difficult to identify an income stream from it. They can use it internally to support income generating projects, but it isn't one in itself.
Anyway, that's my 2-cents worth.
Ian