So you got approached a few times and have seen it happen. Yes it does happen, noone is saying it NEVER happens.
It doesn't disprove the important concept (which I really don't think is an excuse, because it's a fact).
There are of courses times when chicks will approach. For example if they are drunk, desperate, attention wh0res or even if they see you as below their level and so are not intimidated by you. A lot of the time they have an agenda, e.g. they just got dumped by their BF and want an ego boost/show you off to him, need a date for an important event, they need someone to use as social proof to get another guy etc...
But if you sit around waiting for it to happen you are a fvcking chick yourself. That's what they do, they make eye contact and flirt to get a guy to make a move on them.
The guy on the other hand sees what he wants and goes after it. Think how much more chicks are available to you if YOU are picking, not waiting around to be picked. Now understand why chicks get so frustrated - they don't have this option. They can only choose form what makes themselves available to them. So make sure you DO!
Put it like this. You know how an AFC really likes a girl and looks at her all the time but has no guts to talk to her? Or if he talks to her he has no guts to ask her out? That is how chicks act too, they don't make the first move.
That's just the way it is, get used to it.