In a Multi-Cast setup, all web client users are "listening" to the same multi-cast stream, thus the traffic is marginal.
In a Uni-Cast setup, each web client user will have their own data stream coming from the Web server.
So, I would say yes. I know that we have looked at the saizes of our various multi-cast streams and seen them as large as 1mb so depending on the number of users you have, I could see it taking a heck of a lot more band-width. Though 400 mb does seem rather large.