The original purpose of the SRG2105 was to get rid of the old out of date AOPA form that contained spaces for comments on airmanship and the quality of the landing, by people who were probably not qualified to judge. The CAA had occasionally refused to issue licences due to adverse comments. The Certificate was originally an AOPA document which the CAA has now mandated. Its function is to certify that a flight contained in the aircraft Tech logs is genuine. Surely a signature in the pilots log book fulfils the same requirement? Quite odd that they are prepared to accept those documents for a CPL X-Cty but not a PPL!