Flight delays and gate postings

Here's a new one. I'm on AA194 today (SFO-BOS) which was supposed to leave at 1:15pm.

We start boarding 30 minutes before, even though Logan is a mess and everything is an hour or more late into it. Okay, no problem, maybe they expect that by 10pm it'll get better.

As people keep boarding, I'm settled in my exit row seat, the captain comes on the PA and tells us at the air traffic control gave us a 4pm wheels up time and we'll be going back into the terminal and reboarding around 3pm. He blamed our "wonderful" air traffic control system. Now, I know our ATC system is antiquated in many ways and has lots of limitations, but when Boston (and other airports like SFO or ORD) gets behind, there's not much that can be done because of the runway capacity limitations, right? All these planes which are late are competing with the planes which are scheduled to come in later, so the domino effect makes everything late for the rest of the day.

Now, we get off, and we notice that the board at the airport (and on aa.com) changed the departure from 1:15 to 2:15. The GA announces we should ignore that and it's that way because they can only push it by an hour at a time. Huh? If they get 4pm wheels up and they announce that we should come back at 3pm for re-boarding, why in the world would there be any limitation to what they can post as the new departure time???