That's very much true for SF too, though I can understand the temptation. I always feel weird carrying my stuff to the bathroom with me (not to mention if you're trying to save your spot - at Philz coffee getting and keeping a table is a battle).
Yeah, that's why I'd probably ask someone to keep an eye on it, rather than take it with me - I often do that with possessions, although not a laptop, in public situations (cafe, bar, train, etc.) I'd rather live in a society in which we trust each other to keep an eye on our stuff, than one in which we have to take everything with us for a quick pop to the bathroom. Of course, I'd rather one in which the threat of something being stolen didn't exist at all ...
it's gotta be true just about everywhere. in the suburbs, people ask me to watch their laptop all the time (but only when I'm working on my own laptop). And I often see people pack up all their stuff, just to go to the bathroom.