You seem to be underestimating how easy it is to guess beforehand whether or not a stranger would want to talk to you. See the comment thread to this. (Well, I disagree that complimenting a stranger's netbook is necessarily creepy, but...)

Upvoted for an excellent link which caused me to update my intuition regarding the nature and frequency of various types of public harassment of women. I didn't update so far as to regard the XKCD cartoon as "promoting rape culture" (which I still think is going overboard), but after reading the (very very long) comment thread with all the subway/public/other harassment stories, I can totally see where they're coming from.