Ludei told me the file size was because that's the smallest they could make their cocoonjs wrapper (think of it as a browser specifically for your html5 game). When i asked them about it they were quite robust in their defence of the file size to me and, as I'm not a code writer, I have to bow to their expertise.
There is a folder in the apk you can delete if you're not targeting sub-arm7 platforms (i think - found the tip on another thread, use 7zip or equivalent) - I can't remember what it's called as I'm away from my computer but it's pretty obvious and should save you some memory.
Edited for spolling....