We apologise for the inconvenience
When things in IT go pear-shaped, that last thing you want to do is waste time prepping press releases and updates, time better spent ACTUALLY FIXING the problem. You post a message along the lines of "We're currently experiencing technical difficulties. Our technicians are working to resolve the issue, and we will restore service as soon as possible. We apologise for the inconvenience." Then you knuckle down to fixing it.
Distracting the techs with "How long is it going to be" questions simply pisses the techs off and makes it take even longer. People need to realise that when things like this happen, there IS a team of technicians working their bloody arses off to get the damn thing going again. The last thing we need is to be constantly harassed over how long it's going to take, or having some benighted suit threatening to relieve us of our jobs if the problem isn't fixed within the hour. Great - he's going to sack the people who are fixing the problem and take weeks more to hire and train our replacements. Believe me, we want it fixed every bit as badly as you do, so we can put our feet back up and go back to reading and posting on El Reg!
It takes as long as it takes to isolate the problem and develop and implement a solution. Screaming and jumping up and down and threatening to go elsewhere or sack people isn't going to make it go any faster; we're only human and we can only think and act so fast.
So the next time you see an "apologise for the inconvenience" message, picture in your head a bunch of stressed-out geeks running around pulling apart circuitry and frantically coding patches with a stick-wielding boss standing over them threatening to destroy their livelihoods. And CHILL. Don't ask us how long it's going to take. It'll be fixed as quickly as we damn well can fix it!