Having noticed exactly the same thing, I had simply suspected that as Slashdot's popularity has grown it has become inhabited by very young impressionable guys, who's only experience (with computers, but thinking about it - extend that to almost anything) has been with Windows. Being young, male, and impressionable, they need to belong to a 'group' and it's easy to hate - and Apple is a very convenient target. Bashing Apple shows that you're 'one of the crowd' even though you've probably never used any system except Windows in your life. They get hints of what's 'accepted' by the crowd with the story summaries that are often written to inflame discussion to generate page hits.
It's self-reinforcing little world, and as a happy by product, may even encourage some people to use Linux. But what is most frustrating in this theory is the enormous amount of pure blind ignorance being channeled into the Apple hate.
Most of the Apple hate is venomous rants on issues that are at their heart the result of either absolute ignorance or intentional deception. Where you see intentional manipulation, I see a young immature burning desire to be accepted by something, anything. The true trait of a young isolated nerd.
The net result is the same however, and means that Slashdot is now largely devoid of moderating voices provided by experience people who have used more than 2 different operating systems in their lives, and for whom the choice of operating system is the selection of a tool to do a job, not a religion, and who probably have other healthy interests over being a full time nerd.
For other people stumbling across this comment - I'm not trying to flame, really. It's the honest observation of an old timer. One who seriously hope that this cuts too close to the bone of some of the crowd, as opposed to Bonch being correct.