Hazmut, I'm about 99% sure they purposely designed sticky keys to default like this primarily so that people who are disabled would never run into a computer where they could not activate Sticky Keys easily (meaning not having to go into system prefs). Same thing for Windows too. I think I heard this at a CHI conference last year from the man who originally designed sticky keys and the other accessibility apps on both Macs and Windows (Linux and Solaris too now).
Unless you turn off the UA shortcut option, you can always just press shift five more times to turn it off - right? Takes about 1.5 seconds. Still, and no offense meant, is it really that big a deal when it adds benefits for the people who really need it? I mean, they have to put up with OUR lousy and inaccessible designs every single day. A big part of what makes people "disabled" is poor designs that just aren't thought out well.
This can't be happening too often can it? I mean they picked 5 shifts for a reason - it is a VERY unlikely sequence of keystrokes. What the heck are you doing?
Is your shift key set to the high intensity particle neutron plasma canon fire button in some game?
Come on, you can tell us!
You may want to turn on the beep option in system prefs for Sticky Keys so you will instantly know when this happens and can counter with 5 more shifts to turn it off.
Another somewhat related point. The same accessibility expert I referred to above had a demo of all kinds of designs that make life very difficult for people who are disabled. For example, try to open most laptops with just one hand. Most have two latches requiring the use of both hands. Why? Who the hell knows why - it makes no sense and is not neccessary. Meanwhile, Powerbooks and iBooks have a single button to open the lid. I tell you, it is the little things like this - hardware AND software - that really add up in making our beloved Macs so much fun to use. Also, the Mac was the first computer to use a nifty little algorithm for selecting sub menu items - it actually knows that people use a curving motion and not a set of straight linear motions to choose a sub menu item. This is why web pages with sub menu type widgets are so hard to use - browsers + html just can't do the same thing. Of course Windows has the same feature and has for some time, but it is another interesting design point. There are many more that Windows has failed to outright copy because they have yet to really grasp the little brilliant ideas behind so many Mac UI features.