The quality of Xperia’s software experience is dependent on a number of factors including: screen resolution, hardware platform and RAM. In the case of Xperia go, this combination came together in a way that meant the user experience running JB was not adversely affected.
Unfortunately, in the case of Xperia tipo, Xperia miro , Xperia U and Xperia sola this wasn’t the case – so we made the decision to keep them on Ice Cream Sandwich.