I will never forget my first interactions with a team who took this line of argument seriously. They were an outsourced team who had been given a spec for a website. They said they were on track. Our product team went down to talk to them. The most memorable quote was their lead developer saying, "We will just have to train our users to not hit the back button." Almost as bad was, "We have no idea how to support IE." (Over half of our business was IE, and many of our users were casual browsers.)

There is a legitimate debate between rich client-side applications and keeping work on the server-side. Anyone who tells you - either way - that one approach is obviously the right thing to do simply lacks full perspective.

But personally I've been burned enough by people who want to create complex client-side interactions with serious UI mistakes that I have a certain reflexive caution about arguments for pushing everything to the client.

YMMV (and apparently does).