That's very true but I have read on another site, forgot where, that girls doesn't like it when guys have to ask for girl's approval to kiss them.
and to respond to elila's question of how guys get that idea. Well it's simply because of the above. Asking the simple question 'can I kiss you?' and being direct doesn't really work. Also considering that girls tend to do a lot of their communication through their body language that hair test Marker's suggested obviously seems more practical.