My PB is supplied by my employer, so I'm using it all the time in the daytime. Sometimes I have time to do the update, but sometimes I don't - but I might anticipate that I can come to a stopping point in an hour or two. But I don't get that option. If I say "wait an hour" - it will just start the update in an hour - killing my browser and tabs, my IDE, my terminal sessions, whatever else I have open...
Hosed isn't the right word for it - fortunately IntelliJ allows me to continue where I left off, and getting my tabs back is no problem in most browsers. Terminal sessions are jacked, though. And just getting back to where you were mindset-wise - that's a major pain (it's one thing when it's on your terms, but when the rug is yanked out from under you, it becomes a real problem).
Ubuntu (and probably other Debian-based Linux systems - and maybe all of them - so many distros I haven't tried or haven't played with in a long while - sigh) does it right - if you say to try again later, it will pop up the same dialog later. Most security updates aren't of the nature that waiting an hour or a day is going to be a major issue (and if it were, we generally are informed well ahead of time of it).
So - I can understand and feel everyone's pain on this; Apple really should change this to allow user choice. Heck - I'd also love options to install "at next shutdown", "at next powerup", and "at a set time/day" - because at the end of the day, when I shutdown my machine, that would actually be the best time to do the install/update (for me at least).