I am not a web programmer, and I don't use JS and don't plan to use Dart, but I am flabbergasted that a bunch of techies are going wild and posting facepalm pictures over a perfectly normal technical situation. Maybe Google will pare down the runtime in the future, maybe they will figure out a way to exclude parts of it which are not needed, but right now they are just making the default technical choice that just about all compilers make. This is a non-story. Compile "Hello world" into an executable, and see how many kilobytes it takes on most architectures, despite the object file being a few bytes. Geez.
What shocks me is that people who are supposed to be techies are pointing their fingers at the runtime and making monkey noises, because they apparently have never seen a language runtime or heard of the concept. Dart did not compile "Hello, world" to 17000 lines of code; most of that code has nothing to do with the specific program. And that's the usual situation for compilers, although some specific compilers can avoid that (e.g. CoffeeScript, which is a close mapping of its target architecture).
You see, it's not a spherical runtime in vacuum. In practical terms it's more like a whole lot of stuff to download, parse and execute each time your browser hits a new page.
I bet most of the people including JQuery on their pages only use a fraction of its functionality even though it all must be parsed. So what?
Have you actually met any techies lately?
This is called "tree-shaking", is fairly standard, and is on the to-do list. I believe it does some now, but I think more is coming.