For example, Windows Mobile 6 -> Windows Phone 7 -> Windows Phone 8. Is there any phone that you can run the same mobile software on all three Windows phone platforms? No. Each OS version requires new versions and adherence to new standards and APIs. A WP8 app will not run on a WM6 machine.
And that, my friends, was the fatal flaw in the Windows Ecosystem.
I understood the change from 6 to 7. WinMo 6 was just awful. But the jump from 7 to 8 was a deal breaker for devs, myself included.
Trust was betrayed.
AFTER pushing Windows Phone 7 as the "new, next big thing" with the weight of Microsoft behind it, it was then immediately followed, AT THE NEXT MAJOR RELEASE, with a "new - new next big thing" that completely trashed any investment in WP7.
Sorry, that's psychotic behavior, I'm not down for that.