The main reason is the recommended tension of the strings for this racket: it's 54Ibs (Max)
Now I normally string poly's from 50 - 54Ibs depending on the customer / racket specs, but this racket really suits the thinest gauge poly, I have never broken a string even when I go down to a 1.10 mm poly.
This racket and string combination really works, When testing with other types of string it never feels quite right, something is always missing, but when strung with any poly it's like coming home :-)