At my previous job, we were still in process to get session migration to work so servers within a cluster could update while others were running.
At my current job, we don't have a cluster (we have a single over-provisioned server), and that method simply isn't in the budget for the foreseeable future. However, 3:00 AM PDT is 3:30 PM IST (India), which is where most of my team is, as well as the support staff they need (most staff there are on swing shift, as well). Thus, an early morning release is actually a very convenient, as well as lower cost, time to do the release. As the site is mostly US customers in both a B2C and B2B use case, this timing (around 6:00 AM EDT) works very well, and I don't see it changing.
I realize this doesn't scale for a global app, but it explains the lack of pressure to spend much consideration on higher tech, more expensive, deployment methodologies.