Board Thread:Lore Discussion/@comment-72.74.78.209-20141019230536/@comment-9062114-20141027024545

Imperial Propaganda, the Empire knows Ulfric is a popular figure in Skyrim and represents the rebellion to stop them. So by slandering him with these accusations they make his image worse and therefor have more people support their cause, Imperials are known as being very Political and well-spoken so doing this is quite easy. Nords on the other hand are more about Honor, and therefor such a thing isn't as into their culture.