Who was Romney's speech directed to?
In terms of the general electorate, it would seem that Romney would want to make Mormonism a non-issue. If so, then a speech "addressing" the issue would be long and boring with no memorable lines. You'd want people to think, "Yeah, yeah, whatever," and focus more on Romney's tax plan or ideas about coal gasification. A wonkish debate on policy would be what Romney would like.
But he didn't do that. He gave a speech that mixed some explicit Christian beliefs along with generalized deism. And who is that supposed to appeal to? The conservative Christians flocking to Huckabee?
It seems that Romney's speech had modest goals. He was making his pitch to the pundit class and reporters in general. The thinking might be, "Look, we can't change the hard-core conservative Christians, but maybe the low-information Christians will get - from the pundits - a generalized feeling that Romney is okay, and maybe vote for him."