I tried r147 with the sample app, and the same problem happens there.
But I think this is a fundamental limitation of Node WebKit. Node Webkit uses Chromium, not Chrome, and access to the interesting Google services in Chromium needs a Google Dev account and creating a custom build of Chromium (http://www.chromium.org/developers/how-tos/api-keys). Even then, it turns out the speech API isn't public (http://stackoverflow.com/questions/1272 ... speech-api).
I guess until there's a widely available back-end speech API that can be plugged in, what we get is what we have.