Firstly, what has been published are the Implementing Rules (the 2nd level down from the Basic Regulation 216/2008). Below this will be AMCs and GM - Acceptable Means of Compliance and Guidance Material. The AMCs and GM have been developed in a review group at EASA - involving experts from 'industry' over the last year or so, and the publication of these is expected in the next month or so. These do not have to go through the approval process at the European Commission.
Secondly, most of the EU rules and supporting AMCs etc for the LAPL medical are based on the UK NPPL, but the implementation of these will not be linked to the DVLA standards. However, my understanding is they will be very similar. DVLA standards will still apply to the NPPL for those who continue (post April 2015) to fly only Annex II aircraft in the UK outside the scope of EASA.
The 'vagueness' of the Implementing Rules on the LAPL medical is deliberate because at this level it is European 'hard law' and this leaves room for flexibility through the AMCs etc, which are 'soft law'. There are however some specifics in the IRs which mean that the LAPL medical is different in process terms (not necessarily standards to 'pass') compared to the NPPL.
The ability to retain the principle of the GP medical for the LAPL was put into the Basic Regulation during 'negotiations' in 2006-07
The UK CAA medical section has been very closely involved and influential in the whole process, to the advantage of NPPL holders who will need to transition to a LAPL between July 2012 and April 2015 in order to fly aircraft within the scope of 216/2008.