We are all abusing the technologies originally developed for hypertext documents (HTTP, HTML, CSS, JavaScript) for building applications. If you today started working on a set of standards for handling what people currently build on the web proposing those technologies would be completely ridiculous, so ill suited are they for this job. And JavaScript is probably the worst of all, it is designed badly enough that there isn't even a standard way of defining modules or classes so you end up connecting shit structured in a 100 different ways.
The fact that it's still insanely easier to write desktop apps, using one or two languages and a layout manager vs. dealing with two decades of WTF! web programming makes me sad.
See CommonJS and/or AMD combined with a build tool Grunt...
You have component options around, mostly pretty new for building modular JS and building them for use in the browser as a single download. RequireJS in particular goes a long way towards helping with browser development. AMD lends itself more towards the browser, but there are build tools for CommonJS style modules as well.
If I were starting today, I'd probably have a reduced subset of what HTML is, with extension points for form inputs. The issue is that extensible/modular, skinnable and a centralized authority are points of contention for application building. I really liked Silverlight as a concept, I thought the package system was well thought out.
What I really didn't care as much for is how verbose XAML is. I can say most of the same about Flex+ActionScript. The problem is neither of these formats were open enough for browser vendors to simply have built-in support for them as a specification.
I think the problem is that the original technologies were bad to begin with. And the development was ad hoc and without foresight. Just look at the history of the img tag (http://diveintohtml5.info/past.html). DOM was tacked on later, JS was developed in a couple of weeks, with Java-like syntax just bolted on for marketing purposes. And CSS is the worst. Why anyone considers cascading to be a feature is beyond me. I mean, what were they thinking, what was going through the person's head when they decided "yep, cascading, that's what we need, forget name spacing, variables or expressions, we need cascading". Oh boy.
