Most Helpful Guy
Yes, its just much less common.
Same reason - the guy doesn't find her attractive enough to date.
Men seem less interested in platonic female friends than women are in platonic male friends, so she tends to need an unusually good personality.
On the flip side, guys are more willing than women to have random sex with women they aren't that attracted to, which is why the typical equivalent of the friendzone for women is actually the 'fwb only' zone.
There are a few more scenarios that could lead to it, but looks (often weight) is the most common.
Most Helpful Girl
Yes, it definitely happens. And sometimes to fairly average girls and not just ugly and mean ones, from what I've seen. My experience seemed to be fairly common, but I grew up in a small town, too.
I'm not pretty or mean but average in all ways and had a good body then from playing sports, but have a couple of hot friends, so I would sometimes get so-called "friend zoned" by guys who wanted to be with one of them. Not many guys try to sleep with best friends or cousins (I also have many cousins) so things stayed casual. My best friend is very beautiful, so I got used to it.
I've also known a few other girls who particular guys were just friends with because they grew up very closely together and seemed to be more like siblings or cousins.
I've also seen it when a guy has a girlfriend and a girl may like him and he is friends with her, but wants to stay with his girlfriend.