Thats a fair point and I would agree in cases where the landing page won't change or there are not too many variations.

Our ExtJS application has a fairly complex layout and the landing page is dynamic depending on the user type/configuration so there are many variations on what the front page could look like.

We have a fairly large download of 1.2mb for the application once it's compressed so we wanted to show something to users who are on slower connections. I think it's a fair middle ground in our circumstances.