Slashdot is fun. It reports news which basically doesn't exist. This is just some guy who is on an anti-Microsoft bender and wants to somehow make his ideology meaningful in a world which doesn't really give a shit (if the low Linux uptake has anything to go by).
His rant is way too emotional for something that the politicians and most parents won't even understand. I mean, everyone uses Windows right? It's installed on all computers, and if you point at a random computer user, it's probably 99% likely they use Windows or have at least one Windows machine in the house. This is slight hyperbole of course, but it's enough to bet money on most of the time.
Now I'm not saying there isn't value in a open and multi-platform way to distribute information. It's just that this guy overblows the matter. The number of people who would be affected by the requirement for Silverlight is probably going to be EXTREMELY minor. Should those people be penalized? Of course not. But they also made the decision to make life more difficult for themselves by going against the grain and choosing to use something other than Windows (an OS pre-installed on virtually all computers you can buy, so having to buy it yourself is unnecessary).
In other words, if you don't want to use Windows, be aware that you'll be treated like a second-class citizen and it's extremely hard to convince non-geeks (general public as well as politicians) that there's any issue at stake here. Heck, maybe this is part of the reason why people are scared off from using Linux - they see all these posts about "battles" and "fights" that just aren't faced if you use something more mainstream. One could argue that some fights are worth fighting for, but if so... a small petition from a bunch of geeks with too much emotion and too little tact is likely to not do a damn thing.