I agree with the interpretation above, and think the Naples sticky post should be replaced with this one.
Forgive me for stating the obvious, but the Homeland Security Dep't is only just being set up, they don't take over the INS until later this year, and Asa Hutchinson, Under-Secretary-designate for Border Security (who I'll be meeting in a fortnight, coincidently!), hasn't even been confirmed yet, so how can they be an authority on visa waivers?
The linked INS pages on the sticky thread appear to have been removed, but in anycase refer to changing from B1/2 status to student status - if you enter on a visa waiver you're W status so that ruling is irrelevant. The guidance now on the INS site and at the US Embassy in the UK, dated June, (
Bus/Pleasure), states solely that you are eligible for the waiver provided you're from one of the low-risk countries and can demonstrate that you are not an intending immigrant (ie short stay, business or pleasure, have a home to return to), and not proposing "full-time study" (PPL training is part-time even if you interpret it to be study!).
Bear in mind that the visa waiver program has been recognised in recent congressional debate as not posing a threat to the security interests of the US, because obviously it only applies to low-risk visitors, and the economic benefits are substantial. We also have pilot-friendly people in key committee positions in congress, and Asa Hutchinson has in his previous roles been a critic of INS heavy handedness.
It's still the case, as always, that you can be denied entry at the whim of the INS, if they think you are a security risk or likely to stay too long, and with no right to appeal, but there are clear political signs of the non-immigrant admissions regime relaxing again over time.