Dolphins can't smell.

They retain all of the mammal sense-of-smell genes for smelling in air, but they are corrupted by random mutations. None of them function anymore.

Thanks! That would have been useful information for them to add to the article. I assume Hyenas still retain their sense of smell though.

It isn't clear how useful the salty taste would be to dolphins anyway. Wouldn't everything in their environment taste salty, to pretty much the same extent?

The salinity of the ocean isn't uniform and the ocean is connected to various bodies of fresh water. From a quick glance at the map of surface salinity[1] you can see that warmer waters are saltier. Perhaps tasting saltiness sometimes helps dolphins avoid dangerous fresh water, helps to locate different temperature waters, or generally helps them understand the current environment better? Maybe freshwater fish are unhealthy for dolphins to eat?

[1] http://en.wikipedia.org/wiki/Seawater#mediaviewer/File:WOA09...