If you look at the marriages in the original records there are two marriages per page (and in the early days, FOUR; be glad you don't have to pick among four spouses!) When the original indexes were made they just indexed the quarter, district, volume and page; it wasn't till 1911 that they started putting in the spouses' name in the indexes.
Without a computer index of course it was impossible to find all the others with the same volume and page anyway, so what we have now freeBMD has been working away at it is much better than it used to be. Otherwise you'd just have Mary Clarke with no idea who her possible spouses would be. If you're working backwards on other marriages you can use this to filter out things - looking for a John Brown m. a Louisa becomes much easier.
I've heard a rumour going around that the records are going to be reindexed to include spouses surnames for marriages/mother's maiden surname for births/age at death for all records, not just those that are partially done now. But that (even if it's not just a rumour) will no doubt take years.
Until then,
http://www.1901census.nationalarchives.gov.uk/ - with the new way of displaying information (which sort of autosorts into family groups) is a good way of doing quick checks without having to wait for census lookups.
