The reason that vinegar is not mentiond is because Jim H has found that it is not as good as the other activators. Persons dealing with Yeast of Fungus will not do as well with ACV as with the other ones because it is Fermented.
Vinegar is a liquid processed from the fermentation of ethanol in a process that yields its key ingredient, acetic acid. The acetic acid concentration ranges typically from 4 to 8 percent by volume for table vinegar  (typically 5%).
The citric acid sol'n is 10% and the citric acid of lemmons and limes are in the 6 %to 9 % range , so the acid concentration is different also. And there is no fermentation in getting to the acid.