Hot Nerdy Women are somewhat of a weird cultural phenomena. Unfortunately, the video supercut of actresses trying to convince late-night talk-show hosts that they're actually nerds is now gone because it went too viral and the creator removed it because he was getting a lot of negative comments. (Which I don't understand because I thought the video was really interesting.) The article is still there, though.
Ultimately, what the supercut pointed out this weird cultural thing where we see feminine beauty as completely divided from nerd-dom. The melding of these two things in popular culture has been the subject of parody (see the "I'm Such a Nerd" video linked at top), fantasy, and with this supercut, controversy.
The thing with celebrity women claiming (whether or not you believe them) to be nerds points out both a double standard we have with women, and one we have with celebrities.
In popular culture, geekdom is unattractive. This is true for both genders, and unattractive-man-geekiness is definitely way more exploited comedically in nearly every sitcom situation... ever. However, girl geekdom is a lot less common as well as less likely to be "overcome."
This clip from Freaks and Geeks is actually one of my favorite moments from the show... I love Bill. But it's an example of how the TV and movie world construct this trope wherein hot ladies get won over by the winning personalities of their otherwise nerdy BFs/make-out partners/hook-ups, etc. See Michael Cera in anything, Jesse Eisenberg in Zombieland, I Love You Beth Cooper, Sandy in Romy & Michele's High School Reunion, She's Out of My League, etc.
The "Pop Pedestal" post about Mac from Veronica Mars at Bitch I think has a good discussion of Mac's significance as a geek girl character who is 3-dimensional and fairly realistic. However, one commenter on this post pointed out, "I think Mac added a great dynamic to the show. I can't think of any other show that has a female computer geek who also is a legit nice person. Anytime a woman on TV or in a movie is nerdy or better at something than men, she's a bitch or she's not pretty."
Which I think is generally pretty true. I would argue that Temperance, Angela and Cam from Bones and Willow from Buffy the Vampire Slayer are all geeky ladies who are also definitely conventionally attractive, nice, and have 3-dimensional roles, but other than them and TV doctors, there aren't a lot of hot, nice, geeky, female characters. (There are more, I know, but still not a lot.) Geeks in pop culture are often not fully developed characters meant to be more of a bit-part for comedic effect, so really fully-developed, good geeky characters are hard to find. And harder to find when looking for female characters.
With celebrities, we (as in the collective "we") want them to be both real and unreal. It's a disappointment when an A-list woman wears something hideous to a red carpet event and ends up on fashion police, but thousands of people buy copies of Star and Us Weekly to see their fave celebs grocery shopping in sweatpants and without makeup. ("Stars! They're just like us!") Celebs are almost constantly trying to assert their realness in interviews, and when celebrities like Mila Kunis (one of the women featured in the original supercut video that I wish still existed) try to convince audiences that they are in fact nerds for liking Star Wars or video games, that's a version of this "I'm a real person!" If you'll notice, it's much more often female celebrities making these claims than male celebrities. It's also much more common for male celebrity geekiness to be acknowledged and accepted without having to "come out" with it on a talk show like female celebs do.
If someone like Eunice from She's the Man claimed she was a nerd, everyone would believe it. When Mila Kunis says this, people are skeptical because her idealized beauty is seen as a contrasting positive quality to something like Star Wars watching, which is "geeky" and therefore unattractive. And I think you can even separate geeky people/characters from intelligent people/characters because although often connected, geeks/nerds are a particular brand of intelligence that is stigmatized.
And what you get when super-hot actresses claim to be nerds is a divide in cultural nerddom:
The Hot Nerds and the Regular Nerds.
The Regular Nerds are taken as the standard, but when conventionally attractive actresses have nerd-cred, they blur the lines of how we define nerddom and attractiveness. And also provide fodder for nerds sitting at home to fantasize about. But in any case, I think it's a positive thing. I think it's weird, but overall okay. Whether or not all these actresses who claim to love Star Wars and video games actually do, that means that we as a culture can start deconstructing the way we define attractiveness in relation to geekiness.