Original sentence: According to Microsoft, due to platform achitecture change WP7 phones will not be upgradeable to  Windows Phone 8, which will be released in the fall of 2012.Instead, Microsoft will release Windows Phone 7.8, which will include some WP8 features for existing WP7 phones
Edited sentence: According to Microsoft, due to hardware limitations (lack of Multi-core processor, older graphics processor, lack of NFC and MicroSD-support) WP7 phones like the Nokia Lumia 800 and 900 will not be upgradeable to  Windows Phone 8, which will be released in the fall of 2012.Instead, Microsoft will just provide a feature upgrade to mimic some WP8 features on WP7 phones