This is an overblown if not mythical idea perpetuated by SDN and neurotic premeds, who apparently think their peers aren't suffering enough.
1) Applicants who have been waitlisted are plentiful at this point in the season, so they wouldn't be interviewing you unless they thought you might be better than those they have on the waitlist. That said, as mentioned above, the bar may be higher, b/c you have to be better than what's on the waitlist.
2) As schools are going to on average interview their top choice applicants earliest, those interviewed later in the season are probably ones they considered slightly lower caliber, so if there is an increased rate of waitlisting, I would not de facto blame it on the phenomenon of interviewing for waitlist spots, because it must in part reflect the applicants who are offered later interviews.
3) Schools over-extend offers of admission with the knowledge that not all acceptees will matriculate. Once you truly get late in the season I would assume there is a more delicate balancing act as far as making sure the class isn't over-filled, so there can be a need to put desired applicants on the waitlist.
When I applied, my friends and I all received one if not multiple interview invitations after this point in the season. Many of them resulted in acceptances and matriculations.
The amount of worrying that goes on in these threads due to hyperbole and hypotheticals has been increasing disproportionately in the 5+ years I've been on SDN, and so much of it doesn't reflect reality -- don't forget that it's pre-meds perpetuating and exaggerating the "advice" you're getting upset by.