Many many parts are CE marked and contents of the liquids are food grade, so they are already quality checked.
The reason patches and the likes are regulated by the MHRA is because they are a "quit smoking" tool, whereas E-cigs are not and should not me marketed as such, if they are already by some. They are a Nicotine replacement device, a healthier way to get your shot of nicotine, if you chose to use them to quit, then thats fine, but rationing your cigarettes each day, slowly removing one each set amount of days is the same thing.
It's almost certain that they will tax them when they see the billions in tax the cigarette industry isn't bringing in anymore, and thats the only reason there is so much talk about them.