He's also said "(probably) Tuesday". I think they don't want to make any assurances and then have unforseen problems forcing them to delay such a big update. Or they've already run into problems and had to delay it and are unsure if they'll get it out today, or it's in QA and they just hope it passes through today, but it might not. All sorts of reasons are possible.
Fully understand. It's just that impatient kid part of me that is looking forward to it coming out is all... I'm working until 7pm EST today myself (though I would have tried it out during lunch if possible) so it's not a real biggie for me either. Tomorrow, on the other hand, I have off and if it's not released by then I promise to throw a full fledged tantrum in the privacy of my own home.