Thank you David and JasmineA, because you've made me think, and I'd  like to rephrase my question as it follows:

Do the so called "off-site factors" affect Quality Score in Adwords (which affects Cost Per Click) ?

Will I spend one cent less per click if I'd publish my same landing page under the NASA home page (rather than my ordinary domain site) ?

I know landing pages only play a small part in the QS system but even 10% could make a huge difference.

And yes, JasmineA, I have reasons discouraging me from publishing the landing pages under the www subdomain.

Thank you all again.

DoMiSol Rossini