Pandering to the geeks who love the Halo video games eh?
I may be wrong, but one of the prerequisites to use Cortana is to have a Microsoft account. You log in, and along the Cortana learns about your web browsing habits etc.
What annoys me is Microsoft nagging the user to set up or login with a Microsoft account at the end of installing Windows, so you can get 'the full experience of Windows' - one of which is Cortana. Essentially, it is Microsoft's way to push its 'ecosystem' onto the user, and maybe data mine a bit for targeted advertising.
Don't get me wrong, I'll probably get Windows 10 (I am on Windows Vista), but as far as I'm concerned, this Project Spartan browser will only be used to download Chrome and Firefox. I just want a local account for Windows, I don't care for Microsoft's phones and tablets, and I'll use a third=party program (Classic Shell) to keep the UI more respectable.
Anything related to the Internet and online services, I'll stay far away from Microsoft.