You aren't quite seeing the full picture and including some interesting additional bits. The 'experience' of an app across devices - like WhatsApp portable (and then some) - is feasible with what they put in the keynote and what the lesser Scotts did later. It's never been a better time to be a .net/C# dev.

They put on display some pretty great tooling for sharing common code across platforms and tuning the experience per UI. With decent cloud integration, there's a smoother on ramp for C# devs to get to wide audience apps with less dev resource than most any other dev env I can think of.