Reasons not to use MVC architecture for web application

Question

In the past I have primarily built all my web applications using an N-tier architecture, implementing the BLL and DAL layers. Recently, I have started doing some RoR development

Answer 1

I wouldn't use MVC pattern only in the case when I have an existing desktop application built with MVP and I have to convert it to a web environment. That's because I already have written logic for presenter.
In any other case I would use MVC.