Well I don't think the switch from Nokia to Microsoft has anything to do with apps. And as far as carriers go, I was in the AT&T store the other day, and they had the Lumia 830 right out there. In the Verizon store they also have the M8 Windows on display in the HTC section
Unfortunately that won't be true for all stores, went by Carphone Warehouse store at a busy electronics chain last week - Currys (store with-in a store) as I was picking up a HP Stream 11" for my aunt.
All display models for Windows Phone where dead, faulty or turned off and there were not many. Unfortunately it seems my 920 also decided to follow suit as my battery died so don't have any pictures :grincry: (probably a prolonged silence for it's fallen comrades..... it did take a good while to load up again when I put it on charge after I got home lol)
1520 is no longer being sold at Carphone Warehouse (one of the biggest phone retailers in the UK) the only flagship on offer is the 930. So if your after a new high end windows phone with a msd card slot.. your out of luck.
So it is not just in select countries, everything is pointing towards a global end-of-manufacture - not EOL as the 1520 will still get updates. Microsoft would be insane not to push out updates for this phone.