PDF viewing isn't natively supported by any browser as far as I'm aware-- plugins/extensions are required, which makes the content significantly less accessible.

Chrome is packaged with a PDF plugin, which is as close to "native support" as makes no difference IMO.

It works quite well, too.

We use Scribd's viewer inside of Twiddla so that users can pull up documents inside of whiteboard sessions and collaboratively scribble on them.

I'm sure there are plenty of other tools like ours that need something similar.

Frankly, it makes sense to print Printable Document Format documents while showing a user HTML and taking advantage of HTML's features, notably javascript and net use. Of course Adobe put both of those features in, but it's not at the same quality that a native browser implementation can provide.

If you prefer plugin-based reader then it could always be used as a fallback option for those users without plugin. That is if you just need vanilla viewer. Embeddable and configurable viewer would be gold if you want to build more advanced functionality on top of PDF documents.

As someone said in the HN comments for the TechCrunch article, CrocoDoc uses their implementation of a document viewer to support annotation.

Annotation benefits mostly when you view the document again, which means your browser needs to reserve the file for some time like a month or longer, this does not sound like everyone will do.