Other than cost, why doesn't each cylinder have its own head? It seems like that would make more sense maintenance wise, that way when something happens to one cylinder, you don't have to take the whole thing apart. (I know there is an issue with more gaskets and whatnot, but it just seems like it would make more sense - other than cost)
Also, if they were smaller, the size of a single cylinder rather than 4 or 6, etc. then couldn't you put a "screw-on" head, which would allow for a better seal without the risk of blowing gaskets every xxx,xxx miles. I'm thinking like a soda or water bottle, the screws keep everything in (and everything out), or even similar to the screws of the spark plugs.
