Still I don't understand the "exponential" part. I thought that you may have deliberately given an obscure brief answer to the obscure brief question in the OP.
So what happens is that as you search more and more strings, they get weighted exponentially (i.e. like e^-length), so even though the program of length 30 and the program of length 33 show up in infinite strings, when you sum up the total weight, you get two different constants.
Why wouldn't the probability of two algorithms of different lengths appearing approach the same value as longer strings of bits are searched?