"Going south"

I was just watching several commentators on CNN talking about the debt ceiling issue, and what will happen to bond holders if the US defaults. Ali Velshi (sp?) said, "We don't want to alarm anybody, but we'll be right here to tell you if things start going south." (Based on our conversation this morning about people manipulating language, I thought the phrase "going south" was pretty alarming, in itself.) As it's used in slang, it means "moving to a position of decreased value." (Etymology, Old English suth, going back further to sawel, whose derivatives include Sunday, south and solar.) Personally, I don't think this is a derogatory remark about the South, but rather related to graphics. On our maps, downward is always pointing southward. On a graph, when a value is decreasing, it it also pointing downward. This is really just a convention, (in NZ, you can buy -- but they're not generally used -- upside-down maps of the globe) but we all know what "going south" means.