After slashdoters wrote posts like WIndows 7 == Vista SP 2 they had an effect. Many assume WIndows 7 must suck too because that lie was repeated so many times everywhere by XP loyalists. Many are hesitant to change thinking it is just as slow and bloated and that somehow XP will run faster 100% of the time (not understanding algorithm changes and extra optimizations from the compiler added to the kernel for newer cpus).
I seriously doubt that Joe Sixpack goes running to Slashdot for advice on which OS to purchase. Joe Sixpack just uses whatever comes with his new computer. If the latest shiniest Windows sales are down it's because desktop computer sales in general are down. Making Windows go faster is no longer the prime reason to buy a new machine like it was when we referred to it as Wintel.
I did briefly try Win 7 because it came with a then-new laptop I purchased. I was impressed, actually. For Windows, it was great. For Windows, anyway. Sadly, copyright issues alone would prevent MS from ever offering a comprehensive centralized package manager comparable to what Linux distros offer. Having to track down hardware drivers (at all, ever) is a nuisance. Being treated like a dumb user at every turn is definitely a nuisance. The fact that good relatively common-sense security practices are not enough to prevent malware is a showstopper for me. Not being able to poke around under the hood and configure damned near everything, well that sucks. So little choice in desktop environments sucks too. Needing additional software to do what are nowadays basic things (like GOOD remote access, a compiler, etc) that are standard features on *nix is a nuisance. PowerShell is too little, too late compared to what Bash and its predecessors have done for decades (!) now. A binary registry is simply a bad design decision. And while you may find some sense of community among other Windows users, you will not share that with the people who actually put it together.
Slashdot users are more likely to care about some, or all of these things, or something along the lines, than the mass market that drives Windows sales. Here, you may have a point. But every last Slashdotter could boycott Windows forever and it would be a rounding error in terms of MS sales figures. That doesn't explain why Win 7 hasn't skyrocketed the way XP did. It's either ignorant or dishonest for you to pretend that it does.