Phoebe
I hope that you are never at an airport 3+ hours ahead of time and after waiting 1 1/2 hours to check your bags you are told that you have been randomly "chosen" for a hand search. Another line another 45 minutes. Now the security line! But the plane ,knowing what is happening to you, elects to wait a little longer so you can make it.Then the next day you go to check the FT post and see that someone was inconvenienced. It could happen.
IMHO, unless one personally knows that the "late" person was tardy because of their negligence, it's best to appreciate that a pilot and crew were considerate enough to wait a little while. The next time it could be them.