I agree, but I'd just like to add that the quality/quantity of the research/pubs/posters doesn't necessarily reflect the student as a potential researcher.
An extreme example, a lot of research in the physical sciences takes years to publish.
Hell, even biomed science research isn't quick either.
If the PI or postdoc the student works under isn't competent, the student isn't likely to have impressive things to discuss in a poster or show off a pub, even if they've done their job. I'm admittedly a bit biased because I've written off trying MD/PhD partially for this mentioned reason.
I'm at a research powerhouse, but even I recognize that lower-ranked or smaller schools often do not present their students with the "sufficiently autonomous" and consistent research positions med schools love. Summer programs then?
So it sounds like there may be other "factors" at work for the magical formula...
\rant