Answer from cs61c-el (David Tung 16479725) for Question 3
It had to do with the fact that some old hardware didn't take into account the need for a guard and a round digit.  In this case, the most significant digit is in the digits place, while in the other, the most significant digit is in the tenths place (rather, 2^0, and 2^-1 respectively).  If extra digits for more precise arithmatic were not provided, calculations using the first form could potentially be off by quite a factor, especially if x was a small number.