Firsten's fictions

This time, in his "Grammatically Speaking" column in TESOL's Essential Teacher magazine, Richard Firsten, who has a track record for mis-explaining grammar, appears to have taken to just making stuff up. His correspondent asks,

"My friend said, "I'm going to get a sundae," and then she asked me, "How about you?" After telling her what I wanted, it suddenly dawned on me that it wouldn't sound right if my friend had said, "What about you?" Now I'm confused. Are both questions still interchangeable or not?"

Instead of simply saying, "you're deluded" or something kinder like, "either would be fine," Firsten agrees, saying,

"There are many situations in which the two questions What about . . . ? and How about . . . ? are interchangeable... But when asking about what another person wants, it's more common to use How about . . . ?"

Of course, no evidence is proffered to support this strange claim, nor is any explanation given. So it appears to be up to us, the readers, to go out and find some data.

Corpus		COCA	BNC
Total "what about you"		25	9
	asking about want to	14	4
	asking about want something	4	3
Total "how about you"		21	1
	asking about want to	10	0
	asking about want something	6	0

In other words, in direct contradiction to Firsten's confident assertion, what about you is actually more common, even when asking about what somebody wants.

I think I'd like some more scholarship and integrity from this guy. What about you?