I’ve been meaning to answer this question, and my apologies for the delay.
Let’s start with the obvious: all of these websites know their user/reader demographic, and are choosing their layouts, sponsored content and so on accordingly. For example, BuzzFeed has a significantly larger number of female readers than male ones according to this generic-ass graph taken from Alexa.com:
It sucks that I had to show you something with no numbers and all that, but BuzzFeed has blocked the public from seeing their demographic information on Quantcast. If you’re wondering why, just take a look at the information provided about Reddit visitors:
While we’re playing with graphs, I want to point out that Tumblr only has a marginally larger number of female users than male ones:
The thing about comparing Reddit and Tumblr is that you have to think outside of gender. Note the differences in income, age and education level in their users? These factors probably have a much more marked effect on what they choose to post/promote than user gender.
It’s also important to keep in mind that Reddit and Tumblr are almost entirely populated with user-generated content that is then accelerated into the digital sphere by the likes/reblogs/ups/shares of users, and will only be removed by admin’s if they violate the (increasingly limited) ToS of either website. Conversely, everything that goes live on BuzzFeed is approved by… someone. This is what makes snafu’s like that The Story Of Egypt’s Revolution In “Jurassic Park” Gifs post so interesting. [Don’t worry, I didn’t actually link BF, just a Slate thinkpiece about BF! Look ma, I’m #meta!]
Anyway, before I jump on my anti-BuzzFeed (or anti-any website that writes posts they hope will “go viral”, really) soapbox… let’s come back to the point at hand: are these sites gender-slanted? Yes, to a point. But it’s in their favor to exert less effort into appealing to a particular gender than to users of a certain age, education level and economic status.