Sunni brothers normally use "Rathi Allahu Anh" after the name of Sahaba of prophet Muhammad (PBUH). But in many cases use "Karram Allahu Wajhah" for Ali ibn Abi Talib.
For instance on some tiles of Masjid Al Haram there are names of Sahaba, all of them are followed by "Rathi Allahu Anh". But name of Ali is followed by "Karram Allahu Wajhah".
What is the reason for respecting him differently from other Sahaba?