Anything that is important enough in business can have its deadline extended. I think strict deadlines are more about managers trying to save face than an actual need.
I think sometimes strict deadlines are sometimes about coordinated efforts, as in the case of a Superbowl ad. If you're the company responsible for producing the ad, then submitting it a week after the game is unacceptable. I feel like where software is concerned, it's most often like you've said.
Except Christmas. If you're making hardware, there's tons of deadlines you absolutely cannot miss if you want to be stores for Christmas.