The answer to your question is of course no. It's not Digg that is sexist, but those Digg readers who post the dumb comments. Just remember that the most frequent commenters on those kind of sites are the ones who spend their lives posting moronic comments because they have no other life. They are not representative of all society, at least that's the way I think about it. You get one idiot who posts a dumb comment and the rest follow him (yes, it's always him) like sheep.
In the words of Terry Pratchett, the IQ of a mob is equal to the IQ of the least intelligent member divided by the number of members. If you want more extreme examples that prove this rule, try reading some of the comment threads on break.com.