To solve this problem, you must also answer what friends means. There are many definitions.
When you're a kid, you might have kids who live next door to you with whom your parents arrange you to play. At the time, you may refer to these kids as your friends. In retrospect, you may realize they were snotnosed brats who borrowed your toys and screwed them up.
On facebook, friend can mean anyone who requests to be your friend and is not actively objectionable in some way. It can even mean people you would never physically be in the presence of by choice in the real world if you have low enough standards.
In college, it can mean any acquaintance or hanger-on that you spend a lot of time around, even if that's only because they're friends with the same people you are friends with. Strangely, even if you hate this person's guts, you might refer to them as your friend, or you might do the same if you're fundamentally indifferent to them and will never initiate any social contact with them unprompted.
Obviously, it can also mean a person to who you're deeply committed, have great affection for, and do your best to invest lots of your free time with.
Most girls who just want to be friends, in my experience and opinion, mean the following. "You were never in serious consideration to date me. The very idea horrifies me, unnerves me, and saddles me with a lot of damned awkwardness. I'm hot and you're rather troll-like. Do you not know your place serf? Well, I'll offer to be friends because I'm pretty sure your intentions to me were pretty much driven by your genitals, and even if you do want to be friends with me, you're not my kind to such an obvious extent that any time you spend around me will be very short-lived, as my friends won't like you and will make it an exceedingly hostile environment to the point where if you have any perceptive capacity at all, you'll realize to get out. So yeah, let's be friends. I dare you inferior pile of Y chromosome."
-Frank