"Google has offered Native Client and Dart to compete performance-wise, but those are non-standard, Google-specific technologies..."
The conditions surrounding the use of these technologies are no different then SPDY, which is being adopted by Amazon and Mozilla, and is on its way to becoming standardized.
No one wants to use Dart because it doesn't provide any benefits that couldn't also be provided by extending JavaScript, which is something Mozilla, MS, and Google are all working on. This is why no one else wants to implement it, and Google knew no one else wanted to implement it before it was even announced. I'm not even sure if Google intends for Dart to be used, as opposed to using it to try to push specific features through TC39.
No one wants to use Native Client because it will tie the web to specific CPU architectures. Comparing this to ActiveX is appropriate in some way, because it puts additional restrictions on what devices can access the web. If Native Client had come of age at the same time as JavaScript, real smartphone platforms would be probably still not exist, since websites would require x86 processors to run. Intel has only recently announced x86 chips that can provide decent performance while fitting the power profile of a mobile device, and only after getting their ass kicked for many years as the mobile market has continued to grow.