There's no specific reason for the Registrar to be involved. You can't actually register an overseas marriage ceremony in the UK but you can, if you wish, create a record of your marriage at the General Register Office. The Registrar might want to ensure that you will be able to provide the relevant documents if you choose to do so. Alternatively the Registrar might want to make sure that you've got the necessary paperwork to marry abroad (although that's not normally part of a Registrar's duties).
See here
http://www.fco.gov.uk...nd-civil-partnerships
Chris