I think Larian made the title "Flames of Vengeance" instead of the more natural "Flames of Revenge" because the latter is the title of a Rhapsody song.
Then again, I could be wrong.
Personally, I would have said that 'Flames Of Vengeance' was the more natural version. 'Flames Of Revenge' just sounds awkward, to me.
Interesting the difference perspective can make