An ATMega is sometimes a better choice because it's cheaper and uses less power, not because it has a better instruction format. An 8-bit bytecode would be ide

An ATMega is sometimes a better choice because it's cheaper and uses less power, not because it has a better instruction format. An 8-bit bytecode would be ideal for very little on a 64-bit computer (you'd end up simulating larger integer arithmetic that the machine can do in a single instruction, for no benefit); more generally, since the details of the target machine are going to vary anyway, there is no point in having multiple bytecodes with the same underlying memory and execution model that can be easily complied between. Having a C-like bytecode and a Java-like bytecode and a Haskell-like bytecode would be more reasonable, but it would also be a huge pain for browser makers. One highly optimized VM is complex enough...