Furthermore, in critical phenomena one is often trying to calculate the critical exponents, which should be independent of the details of the system (often called "universality"). In a typical interface problem, one is trying to calculate the interface position essentially exactly, so that one cannot "hide behind universality".
Moreover, in critical phenomena, one typically calculates the critical exponents, which are supposed to be unaffected by system details (often termed "universality"). For an ordinary interface issue, one endeavors to ascertain the precise position of the interface with such accuracy that reliance on universality is not feasible.