Samsung's browser (and several other competitors) are faster on Android because they contain closed source rendering that's customised for their chipsets. Google can't integrate the closed source code into Chrome because they'd effectively have to fork it from Chromium to do so.
Doesn't Chrome already contain close source code? I thought it was chromium plus Google proprietary code. For example, some features are available only on Chrome (DRM etc. "features"). If they wanted, they could optimise for a selected few top selling devices.
