Well, I wasn't there so idk about that, but it looks like 3/7 of the "most important announcements of build 2016" are directly related to windows 10 mobile ^[1]
1. "Microsoft is launching its latest version of Windows 10"
(you realize this is for pc and mobile?)
3. "Facebook committed to bringing native apps to Microsoft's Universal Windows Platform"
7. "Windows 10 Mobile users will be able to "beam" Continuum sessions to compatible monitors."
The point I take from this is that they seem to be considering windows 10 as one platform (desktop and mobile), which makes sense to me since the several apps I've written for UWP worked on mobile/desktop with the same code. Also I think the react-native-windows news isn't listed there, but I personally consider it fairly huge news for win 10 mobile (and desktop) as someone who uses react-native for android / ios
Well, I haven't used the 620, but my anecdotal experience has been the opposite.
List of recent devices I own that are unbroken:
lumia 521, 950, and Kyocera Rise.
broken:
nexus 7 (screen after 2 months), asus fonepad note 6 (screen after ~1 year), galaxy s4 (won't connect to tower, probably my fault for installing roms incorrectly)
In particular the 950 has been dropped in the river in breckenridge, and the 521 in a natural hotspring / taken on many rainy hikes / dropped more times than I can count.
My 820 took one hell of a beating over the time between purchase and replacement. Its replacement seems pretty hardy too. Though I get the impression the build quality and sturdiness were far more variable between models than found around the 3110/3210/3310 era.