Making that illegal would lead to airlines announcing delays in 10 minute increments, even when they know 90% that its going to be 1+ hours.
I know when that happens know and everyone (myself greatly included) hates it!
GA: Looks like we're going to be about 10 minutes delayed to fix a loose screw.
<ten minutes later>
Still trying to get it good to go, be about another 10 minutes
<ten minutes later>
Looks like the mechanic says we're going to need to bring in a different aircraft and that will be about 10 minutes
<ten minutes later>
Waiting on the tug to get our old plane moved
<ten minutes later>
You get the idea. Not fun times...just tell me you think its going to be 2 hours, and I"ll keep checking my app for an updated time.