> But, but ... isn't every estimate supposed to be provisional?

Heh, no. It is an estimate when you are making it, but ten minutes later it magically becomes a commitment.

"Tasks like this usually take two days, sometimes one or three, very rarely more... so, two days on average."

"Okay, I am writing down: two days."

...two weeks later...

"How it is possible that the task took three days when it was estimated at two? You made the estimate! And you all were there at the planning, and no one said anything! As senior developers, you should make better estimates, this is unprofessional."

In an ideal world, yes, especially if requirements/scope/environments change. But the world is often not ideal. Often unless there is what they see as good reason (the definition of good may vary widely), managers & business planners don't like estimates going up in the short/medium term and pressure to try stick to the original estimate may happen.