While they now support newer versions of Chromium (http://code.google.com/p/chromiumembedded/wiki/BranchesAndBu...) it is likely that Valve either didn't have the time to test everything against a new Chromium revision, or didn't want to take the risk. Every Chromium commit historically has a very high risk of breaking embedding use cases (I used to try and track Chromium for my own embedding purposes before finally giving up because it broke constantly).
As far as Chrome on Android goes, I have no idea. In Google's case you would expect they would have the resources to keep up with changes to their own codebases.
http://code.google.com/p/chromiumembedded/source/detail?r=60...
While they now support newer versions of Chromium (http://code.google.com/p/chromiumembedded/wiki/BranchesAndBu...) it is likely that Valve either didn't have the time to test everything against a new Chromium revision, or didn't want to take the risk. Every Chromium commit historically has a very high risk of breaking embedding use cases (I used to try and track Chromium for my own embedding purposes before finally giving up because it broke constantly).
As far as Chrome on Android goes, I have no idea. In Google's case you would expect they would have the resources to keep up with changes to their own codebases.