Mobile devices are nearly on par with where that plateau began, and there are plenty of reasons to increase the CPU/GPU performance for the purpose of games. In this context, it certainly appears to me that Amazon is wasting their resources on what amounts to a massively complex privacy snafu.
It's true this problem is also being solved by LTE rollouts but those aren't today for most people.
Some day, sure, they'll ship with 3G connections. But client hardware on future devices will only be faster and more capable.
A SPDY-link to Amazon's private caching/compression network is a great win and differentiator. But why even open the can of worms that is two-tier _processing_?
If they're leaving flash enabled on Silk, surely that dual-core chip is capable of keeping up with the bulk of browser rendering and js tasks.
http://www.fcc.gov/measuring-broadband-america
I forget the exact numbers off the top of my head, but I just remember it being really difficult to actually find the statistic. But the takeaway is that although we are theoretically #27 in terms of broadband speed, our actual broadband speeds aren't that much lower than in other countries.
edit: http://www.akamai.com/stateoftheinternet/
The Akamai report here is probably the most credible source. I remember there being one other report that covered this info, but I can't find it right now.
Danger, Opera, and Blackberry have all done this with lackluster results. Mobile Chrome has the chops to handle the modern web. This kind of pre-rendered solution might have been a good idea 4 or 5 years ago, but now its questionable and brings up issues of privacy, vendor lock in, EC2 issues (hi, my website was down for 48 hours a couple of months ago), EC2 load issues, etc.