If you are a windows 10 user and use cortana on desktop, and xbox one user which is likely to get cortana, you will have one personal assistant across all your devices. Is it a clear benefit, it entirely depends on your use case. As Windows 10 notebook owner, even though I mostly use Cortana on my phone, she/it has enough context when I use her on my notebook.
Problem is Microsoft will likely abandon Cortana before very long, like they've done with SO many of their products.
Plays4Sure, the original Surface, Silverlight, I could go on. MS has no stomach for long-term commitment to their non-core products, and as such I'm always counting down the days till their latest innovation/copyvation gets the ax.
All of your examples (maybe with the exception of Plays4Sure) were consumer flops. Silverlight could never beat Flash and wasn't highly adopted. Surface/Windows RT was lambasted by the media and confused customers. Plays4Sure was moved into Certified for Vista then eventually killed off when services that were using it were also killed off. Meanwhile, there's been more than a few services and products that lived well after their prime, Silverlight really being one of them. The fact that XP was supported for 13(!) years in a tech world is crazy.
But really, what do you want a company to do when it has a failing product that isn't getting traction? It's unreasonable to keep it on life support for years for absolutely no reason whatsoever.
