Silverlight *doesn't* suck.
It's actually pretty awesome. The biggest complaints I've heard about Silverlight is that doesn't run on everything (but neither does Flash) and it doesn't have a big enough install base (but that's the same with HTML5).
Flash isn't so awesome, in a lot of ways. But it gets the job done. And it was around when there wasn't much else to pick from. It is popular. It was also buggy and insecure, but it become the dominate force. Flash isn't 'open' and it doesn't run everywhere (just like Silverlight).
When Silverlight was introduced and in it's early years, there was no HTML 5. Microsoft didn't create HTML5. Remove HTML5 from the equation and you are left with Flash Vs. Silverlight Vs. Java Applets. I'd pick Silverlight, even if it goes less places than Java Applets.
But HTML5 is gaining support. A lot of big names are on board. It's generally recognized as the 'future'. But the future isn't here. HTML5 isn't even finalized, support on the PC is pretty good assuming you've got the latest and greatest browser. But if you don't (how many people still run IE6?) or if you have a portable device odds are you don't have HTML5 support. And, HTML5 brings back a lot of problems that Silverlight, Flash, and Java attempted to solve. If a browser doesn't implement HTML5 correctly, you can see different behavior in different browsers. Even it is considered a 'bug', it's a possibility. A lot of browsers don't have FULL HTML5 support, which is, again, a problem. Things like 'I want to play this video' is a difficult task in HTML5. Different formats are supported by different browsers.
Still, don't think MS didn't want Silverlight to become the next big thing. Also, I'm quite sure any Silverlight application you've written will continue to work for the foreseeable future. I really believe that if you've created some compelling content worth seeing, users will click on the 'Install Silverlight' button. It's pretty effortless. Certainly less effort than getting your user to upgrade to a new web browser.
I understand the frustration Silverlight developers might feel, knowing that the web is going in the direction of HTML5. But that is beyond MS's control. It's probably the exact same feeling Flash developers are going through. But I can't fault MS for adopting HTML5 for a new website they are making. I don't see how that is 'stabbing' someone in the back. I've written some things in Silverlight and I never paid a single penny to do it. I think it's pretty ridiculous the level of entitlement some people have.
"Hey - here is this cool thing we spent years developing. You can use it. It's free. Also, here is some software that also took years to develop that you can use to create things for that first thing we were talking about. It's also free. And here are all sorts of examples and documentation we put together. It's yours - free! You can use it, or not, it's up to you."
Five years later....
"OMG! What a bunch of jerks. First they BEGGED ME to write apps in Silverlight. Now, some new technology is in the spotlight and my existing code works exactly like it always has but BOY AM I ANGRY! Microsoft Sucks!"