I recently attended a funeral at an Episcopalian Church. During the homily, the priest said something like the following:
"We don't know where Bob is now, since that is a mystery to us. We can only have faith that he will enter into the Lord's rest and have repose with all of the saints."
The candid way in which uncertainty about the afterlife was admitted was somehow refreshing. I can't imagine our leaders saying "we don't know..." over the pulpit about much of anything. So I started wondering why this is and can think of a few possible reasons:
1. One of the key points of the Restoration is that truth has been restored in its fullness in the latter days. Admitting any uncertainty in doctrinal matters may be seen as undermining this core premise of the Restoration.
2. The clergy at mainline churches generally have extensive formal training and practice their calling on a full-time basis. Perhaps that makes them more secure in admitting ambiguity in doctrine (i.e since many of the laypersons can't really challenge them theologically). LDS leaders are put into their callings without much formal training, so admitting uncertainty in doctrinal matters may undermine their authority a little too much.
3. It is acceptable in our church (though I don't think in others) for leaders to suggest that personal revelation is the appropriate sphere for more speculative doctrines. It is probably easier for a leader to suggest that members pray about something themselves rather than admitting that they aren't sure about an issue.
(Another post might address the interesting reasons why the public face of some mainline churches (let's say Episcopalians, Presbyterians, and some Lutherans and Methodists) seems to offer a message that is extremely light on doctrinal content.)