The context might be to discourage people from applying ED under the mistaken belief that it improves chances of admission, particularly if there are factors that could strengthen an application later.
Applications submitted RD might be different than the ED application because of differences in the application itself – things that happen over the course of the first half of senior year that present a different picture.
A big difference between ED & RD is the opportunity to see the mid-year grade report. It is of course possible for an ED applicant to be deferred because the ad com wants to see the fall semester grades, but if there is nothing particularly distinctive about that applicant – no particular reason to hang onto them either. But with an RD applicant with strong fall semester grades, the issue that might have been of concern in the ED round might not even be noticed in the RD round. (Let’s say hypothetically the kid seem to have an “off” semester spring of junior year - not horribly bad, but more B’s than typical of the rest of the transcript - but fall semester senior year is very strong. In the ED round the fall off might look like a worrisome trend; in RD, with fall grades in hand, it looks like a minor blip, one that might even be explained by a letter from the g.c.)