For some odd reason, I just remembered that Mr Wizard did a similar experiment.... oh... 20 years ago... using sonics on a glass of rootbeer? Something like that, with a similar experience.
I've never really had a problem pouring a glass of Guinness, but all the local pubs are useless. Either I'll get a glass that is 50% head, or no head at all. And the bartenders do not like being told how to do there job.
I wonder if the purger had lazy, ignorant bartenders in mind. Pour a Guinness half-assed, then just "purg" it for the head.