Will Windows Phone 7.5 Devices Run Windows Phone 8 Apps?

According to Terry Myerson, the Corporate VP of Windows Phone, all Windows Phone 7.5 apps will be compatible with Windows Phone 8, and The Verge recently reported this same stance from Microsoft PR.

“We haven’t announced Windows Phone 8, but in terms of I can show you our goal to all Windows Phone 7 applications will run on Windows Phone 8. Application compatibility is always something, where there’s always stuff on the fringe…. The spirit is our goal that all Windows Phone applications today run on our next release.” - Terry Myerson, speaking to the financial analyst community at Mobile World Conference (via Mary Jo Foley at ZDNet)

Assuming that the insider sources for The Verge, Mary Jo Foley, and Paul Thurrot are correct, current Windows Phone users have to accept that Windows Phone 8 is simply not coming to *any* current Windows Phone. Yes, this is horrible news, and Microsoft deserves all of the criticism and flack they're receiving about this. Anyways, my question is, since WP8 is looking to be so vastly different than WP7 (different kernel and all), will apps made for WP8 work on WP7.5? Say Instagram or Draw Something is made for WP8, will those of us stuck on WP7.5 with no upgrade path to WP8 be left in the dust? If so, I will be extremely disappointed, and I don't think I will be alone.

Not being eligible to upgrade to Windows Phone 8 on my still very new Samsung Focus S would be quite the bitter pill to swallow, but missing out on popular apps that don't work on my new phone would make me think twice about ever purchasing a Windows Phone again.

Source: ZDNet: Reading between the lines: Office on iPad, Windows Phone upgrades