Why does .2.2.2 in Spotlight equal 0.0016?
It's supposed to be multiplication, which in scientific notation is signified by placing the operands adjacent to one another (operators such as "*" or "x" are optional). I say supposed to be multiplication because .2 times .2 times .2 equals .008, not .0016 as presented in your question. I suspect you didn't gather the entire string for your title, and another .2 was present.

Your screen shot, on the other hand, correctly gives 0.000064 as the result of .2 * .2 * .2 * .2 * .2 * .2. Since that operation is the same as asking for .2 to the sixth power, entering ".2^6" into spotlight will return the same answer.