The 70 hours PIC required is for licence/rating application and does not prohibit the test being taken earlier.
One can not take the skill test until one has the experience required for the issue of the class rating;
Appendix 1 to JAR-FCL 1.130 and 1.135
SKILL TEST
6 An applicant for a skill test for the PPL(A) shall have received instruction on the same class/type of aeroplane to be used for the skill test. The applicant shall be permitted to choose to take the test on a single-engine aeroplane or, subject to the experience requirement in JAR–FCL 1.255 or 1.260 of 70 hours flight time as pilot-in-command, on a multi-engine aeroplane. The aeroplane used for the skill test shall meet the requirements for training aeroplanes (see Appendix 1 to JAR–FCL 1.125).
JAR FCL 1.261 covers where the training for a multi engine class rating must be completed.
When one applies for a PPL one is applying for two things - the issue fo the licence and the issue of the rating / ratings that are to be included in that licence. There is no reduction in the requirements for rating issue simply because it is being done at the same time as licence issue.