As for L2B your belief is incorrect, they just didn't look closely at reg numbers.
As for L2B I believe the organisers asked for MINIs to join in and last year out of 100% only 5% were new so yes that's taking over! And as it first come then it's up to them how many are let in.
Not completely sure what is mean't by your statement but just for the record my local club the London and Surrey Mini Owners Club (LSMOC), organisers of the L2B, are a MINI friendly club and have always actively encouraged MINI's to enter the run and show 'n shine, etc. and next year the event will be jointly sponsored by Miniworld and Modern MINI magazine...........
From LSMOC website:
New Mini
Just a short note here - the club is founded on promoting Mini-motoring, safe motoring, fun and friendship. Any enthusiast is welcome. We have a wide range of opinions in the club which we believe is healthy, ranging from those who are die hard Classic Mini enthusiasts, to those who already own both Classic Minis and New Mini. We welcome those who wish to join us in having fun.
The London & Surrey Mini Owners Club is one of the largest Mini Clubs in the UK.
The Club exists to offer owners of all Minis, from 1959 to the present day, an opportunity to have fun with their car.
Your car may be a pristine, concours quality machine or it may be suffering from years of abuse. It may be straight out of the MINI showroom or it may be in hundreds of boxes in the shed. We welcome anyone who has an affection for this great little car.
http://www.lsmoc.org/