
7.8 will be available for current Windows Phone devices, including popular devices like the Nokia Lumia 900.
Windows Phone 8, on the otherhand, will be deployed on newer and more powerful devices.
The following is missing from 7.8:
Over-the-air updates
Support for screen resolutions higher than WVGA
Internet Explorer 10
Multi-core processor support
Windows Phone Wallet
NFC
Real multitasking
MicroSD card support
Device Management
Company Hub
Secure Boot and Encryption
Check the document here:

Written by: Andre Yoskowitz @ 13 Aug 2012 21:23