We're talking about deployment to production machines - what's the difference between 3 seconds and 5 minutes? Your machine is sitting on a fat pipe in a datacenter, where you can push a 300MB deploy (which is a LOT) trivially. I highly doubt you're rolling out code changes every 10 minutes... not to production anyway.

Sending diffs removes your ability to roll back at all, or if you're somewhat devious about it, it still wouldn't allow you to roll back more than a single version.

I'm surprised you're so concerned about time-to-deploy for an action that happens, what, once a day at most? Twice? The amount of safeguard you gain for the trivial non-human-time (it's not as if some guy is sitting there copying files) increase is pretty massive.