look at it this way. Google has a master plan for its Chrome browser that quite frankly does not include the needs of other linux distributions or their users. Chromium the project has a codebase which is the leading edge of that plan for Chrome the product.
Do you really think that ChromeOS is going to have a browser with this sort of rate of churn? The rapid rate of development for Chromium right now has a lot to do with Google's overall plan for its own product line. They have real consumer device targets in mind for Chrome and ChromeOS and what you are seeing is the development run-up towards very specific end-goals.
Lets face it, other linux distributions are not the target audience and are not driving the development curve. But the development curve does make sense if you look at stable ChromeOS deployments as the end goal for the rapid development push that is going on now with Chromium. We can get as mad as we want about the reality of that, and its not going to make any difference at all.