We trump your density. We don't know how to give signals.
Either that, or we thing that burping the 4th movement of Beethoven's 9th is an obvious sign of affection.
That said, most guys won't become friends with girls they aren't at least remotely attracted to. Yes, there are a few pure souls out there that aren't as judgemental... but good luck finding them. As all rules, there are many exceptions to this rule, but more often than not, they have at least an inkling of interest... even if they don't know it. Hell, even if they've never considered it.
Looking back on my past, most of my female friends were girls who I would have happily agreed to go out with... even though the thought had never crossed my mind at the time.
Call it roughly 85%. Those are betting odds.
I'm not suggesting to be paranoid... but it probably shouldn't be such a shock.
In conclusion, a response to >>13
Man, at that point it's all or nothing. At that moment, you've tossed away all the years of friendship and you've got nothing to show for it... unless you show her how serious you are about it and jump for it. Time is not on your side in that situation.
It's one of those rare situations where you just have to talk and keep talking, because the moment you stop and say goodbye, you've lost. Unless you can get her to open up at least to the possibility of becoming a couple, you've lost, because after that, the entire relationship is one big 'ol awkward silence, and there's no getting around that without just saying goodbye for good.