I think they've been at it for a pretty long time with old products like Dragon. A friend used to work there some years back and said they pretty much perfected speech detection up to some very reasonable error rate. I imagine they've just continued to cover all the dark corner cases and irregularities and accents etc.

The biggest leg up they have is that their product works in a very controlled domain. Siri is out there trying to be a complete interactive AI human and failing miserably. The Xfinity remote just controls your TV and does it smashingly. I found the Alexa-driven voice control on my FireTV to also be a pleasant experience compared to regular Alexa.

Ironically, Siri (as a virtual assistant) came from SRI's Darpa program "CALO" back in the 2000's. SRI also has a speech recognition platform called EduSpeak, and that is the codebase that was licensed to Nuance for their product.

However, after Siri was sold to Apple, I don't think that they retained the EduSpeak portion for speech-to-text. (I honestly don't know - but it seems to me it did not; I don't think Apple wanted to pay that license fee to SRI).

The TV remote only has to understand TV-related things, like inputs, channels, volume, and program names. Siri and Alexa have to understand everything.

I use Siri every day. Former radio guy. Siri is horrible even for me