This is what happened with Microsoft and IE6. IE6 launched in 2001. Microsoft didn't care updating it for the next 6 years. This lead to a rise of Flash in websites, which at the time seemed like a good solution to fill the lack of support of CSS. But then it also lead to a lack of innovation in Flash, and Adobe never cared about its plugin optimization or security.
Adobe never cared about its plugin optimization or security
But why should we blame monopoly? MS had no competitor in the desktop space (even now, OS X has like 10% and Linux around 1%), and still they improved Windows continuously from 3.1 to 8. Same for Office. After the demise of WordPerfect, it never had any serious competitor --even today the vast majority of people choose it over the free OpenOffice, whereas Google Docs have insignificant user share (from what I've read). Still, MS continuously added things to do. Same for Photoshop, Illustrator, etc. They did not have any competitor, especially with Macromedia acquired (Corel's software is not used by the majority of graphic designers, and almost nobody uses Gimp outside of Linux), and yet, Photoshop just received it's most substantial update to date.
So, monopoly != necessary stagnation.
IndexedDB - Chrome Mobile has it (outdated version), Android and iPhone do not.
Chrome will have Dart support at a later date, no other WebKit vendor is going to implement it.
There are literally dozens, just go to caniuse.com and play around for a bit.
I've probably missed some killer feature of a multi-engine standards-based ecosystem, but really -- is that the pace at which we want to move the web forward?