Well, yeah -- the people who are going to object most strenuously to a huge UI change are those who are invested in the current interface, and are going to have to waste a lot of time relearning things the 'new way.'

But they also tend to be the people most invested in the software itself, so if you're a company that sells software you should probably torment them at your peril. Drive them away without successfully luring any new users, and you may not end up with very many at the end of the transaction.