We differentiate ourselves from the Android Speech API in several ways:
1) As a developer, with Google you have no way to customize the speech engine by providing your language model. Wit.ai builds a specific, customized configuration for each app. If your app is specific and you cannot tell Google what kind of thing it should expect, accuracy will be bad especially in noisy environments. Wit.ai builds a specific language model for each app automatically and in real time (each time Wit.ai learns more examples about your app, it's updated), and queries several speech engines in parallel. To do that it uses not only your data, but also relevant data from the community. This is the core of our value proposition and not something Google does provide today.
2) Google keep their Natural Language Understanding layer (what translates text to structured, actionable data) for themselves. Developers cannot access this. They're left with free text, but they often need actionable data.
3) Wit.ai is cross-platform. We have SDKs for iOS, Android, Linux, etc. [1] or you can just stream raw audio to our API. Android Speech API is just available on Android (well, you could hack it and use it from elsewhere but you're not supposed to, and you can be shut down anytime). More and more wearables and smart devices will run Linux. For instance hundreds of developers use Wit.ai on Raspberry Pi.
As for the Apple doc you linked, it's Mac only (no iOS) + it just recognizes a few phrases you provide in advance. I think it's a very old API that's still here :)
Regarding listen.ai, yes please we would love to have Google (especially Now) there. We have the Siri founder, the top Cortana guy, the former CEO of Nuance... but nobody from Google yet.