here's a copy of it:

http://www.deseretnews.com/article/590038317/Text-of-letter-from-First-Presidency-on-guns.html?pg=all

"Churches are dedicated for the worship of God and as havens from the cares and concerns of the world. The carrying of lethal weapons, concealed or otherwise, within their walls is inappropriate except as required by officers of the law."

This suggests to me it is not about liability so much as dedicated houses of worship. To the extent dedicated houses of worship is the justification (and not a pretext), I'm not sure what application this has outside of church buildings.