Hidebound Banners

I've been working on a Christmas banner campaign for a client, yet again coming up with creative for the usual banners (468 x 60 pixels), MPUs (300x250 pixels) and skyscrapers (120 x 600). This has led me to wonder why we're stuck with the same formats that we've had for years. Trying to get a message across in a box 468 by 60 pixels in an era of broadband media convergence just seems ridiculous. I mean, why is it 468 pixels long anyway? Seems entirely arbitrary to me (if anyone knows the reason, please do tell).

Of course, it could be argued that the formats fit around content rather than intruding upon it, thus satisfying usability requirements. However, why not have widescreen MPUs to accommodate movie trailers? Or fat banners that do something similar? They could still sit on the periphery of content, but deliver an experience that would actually entertain users.

For a young medium the internet already feels terribly hidebound in some of its traditions already...