They're sort of there...
There's one store which holds apps for each platform, VS now generates apps for each platform, but... the APIs are still different although maybe less different than in Windows 8 and a desktop version and a TIFKAM version of the same app will still be as different as chalk and cheese.
How does that work in the code then? Spaghetti programming held together with ifs? Huge abstraction classes for each device type?
Still, to all intents and purposes most users now think the same version of Windows is running on loads of different devices and the same app runs everywhere. Yay, Marketing's done it again.