Obama on same-sex marriage

Barack Obama speaks out and declares support for same-sex marriage - no real surprise there. I'm not sure what to make of the following sentence of the article though:

Obama said he had long supported civil unions but his position on same-sex marriages had been evolving because of the powerful traditions and religious beliefs attached to the word marriage.

My personal view is that given government acceptance and support of common-law relationships combined with the current state of family law and no-fault divorce the government has de-facto been out of the marriage business for some time - reserving only the term. If this is listed as due to "religious beliefs" attached to the terms why not let the religious institutions deal with whatever they want to call marriage and instead get the government out of the marriage business?