The amount of space it takes to encode that difference puts a bound on the number of such differences there can be.

For a given description length, yes, but since there is no necessary bound on description length, there is not a necessary limit to the number of possible differences. As your description length devoted to 'comments' increases, you can make the responses and circumstances ever more specified, multiplying the number of worlds which resemble the simpler world, relative to the more complex one.