I think that Mad (Flt) Scientist and Keith.Williams have "nailed it" quite adequately, with MFS emboldening the original clue contained within your own post (This is particularly so at higher field elevations and temperatures).
In a typical certification scenario, the worst case Vmcg and Vmca are established, and, if after applying the required margins, the required V1, Vr and V2 are not affected, the process is complete. If, however, Vmcg (or Vmca) is a problem, the regulations do allow the manufacturer to make application to the regulatory authority to consider the lower Vmcg and Vmca at higher altitudes.
In the latter case, the revised V speeds can be presented in a fairly complex form, or alternatively, by simply adding the words "If V1 calculated is below Vmcg, V1 must be increased to Vmcg".
It is far easier to add the "If V1 calculated is below Vmcg, V1 must be increased to Vmcg" caveat than to prepare and present a more complex V-speeds table or graph. This does not mean for a moment that the Field Length and Obstacle requirements are sacrificed in favour of a controllability problem. Within the Field Length and Obstacle calculations it HAS been considered, and a fairly standard V-speeds table presented in association with the caveat mentioned.
This has nothing to do with the "grandfather clause" suggested for a 1962 aircraft, the simplified system of adding the caveat continues to be applied on more recently certified aircraft such as the B777.
In westhawk's original post mention was made of requisite margins above VMC -
V1 must be equal to or greater than Vmcg,
VR must be equal to or greater than 1.05 Vmca, and
V2 must be equal to or greater than 1.10 Vmca.
Regards,
Old Smokey