@PotomacBobFrom Grammarphobia.
In the sense of "await," both "wait on" and "wait for" have long histories of usage in English, both in Britain and in the United States.
In general, "wait for" is more common, but "wait on" is part of mainstream usage in both countries.
In the US, according to Merriam-Webster's Dictionary of English Usage, "wait on" is "most strongly identified" with speakers in the South and the Midwest, though plenty of Northerners use it too.
"If it has been the mission of Northern teachers to stamp out wait on, they have failed in more places than just the South," the dictionary adds.
Another source, Merriam-Webster's Collegiate Dictionary (11th ed.) has an interesting thought: "One reason for the continuing use of wait on may lie in its being able to suggest protracted or irritating waits better than wait for."
The dictionary gives several examples to support this idea, including one from Charles Lindbergh: "for two days I've been waiting on the weather."