Well I'm not sure about the hardware independent part - as otherwise they would have got it to run on the BT Vision boxes. There was an endless debate with the main sticking point being the lack of DVB-T2 tuners. Even the mods confirmed that the BTV boxes would run YouView at one point. But now instead we have BT Vision 2 and BT trying to support BT Vision Classic, BT Vision 2 and YouView whilst implementing changes to BT Vision 2 to give linear channels. It's no wonder things are a mess at the moment.
Well I'm not sure about the hardware independent part - as otherwise they would have got it to run on the BT Vision boxes. ....
Hardware independent as in its not tied to one specific device from a single manufacturer, sure there are a list of minimum prereqs and the BT Vision boxes don't meet them, but the same Youview software runs on the Humax box for BT as runs on the Huawei for TalkTalk and will run on the Pace (once they iron out their issues).
Key point is that the manufacturer has not written the top layer of software stack, only the pieces at the bottom that abstract the hardware services away. Where manufacturers do the whole piece they rarely offer significant upgrades and extra functions, because they want to flog a new box for that, with the separate Youview layer there is good reason to belive we will see a stream of extras come along (because they need to support commercial partners).