OMG, colo. I've been the architect of a Top 500 website acquired by a Top 100 and even for that we just rented a few servers (you'd be surprised how few -- a dozen or so). I do not really know how big you need to be make colo a sensible choice but quite probably much, much bigger than most think of. We ran the numbers and they weren't pretty.

And for cloud: we purchased video conversion as a service, that one ran in the cloud. I can see how that makes sense.