Maybe because this model is high end and the request for it is low. Although i3 is a powerfull processor and i think is suitable for an 13" display. Why would you need an i5 or i7 processor when you can't do designs or something that would require more power... For me would worry more the graphic card witch is integrated. My conclusion is... if you go for a proper work station i would give up mobility and design.
Thanks for the reply. You are generally right. And i couldn't agree more with the graphic card issue. That's just stupid for this century. I really don't get some Vaio models. So much attention to design details but so little investment into things that matter a greater deal.