On 20b, the level of "chasivus" of meat versus poultry and fish is ignored with respect to what is included in one's "neder" who is "noder basar". The "Chachamim" are concerned only that all three of these foods are "minai basar". At the end of "parshas Pinchos", Rashi cites a Medrash that a host can learn from the diminishing "parei hachag" to similarly decrease in "chasivus" from day to day what one serves the same guests. "Ptumos" are served first, followed by fish, followed by "basar". Thus, "Ptumos" and fish have more "chasivus" than "basar". Presumably, the "Chachamim" ignore this factor when addressing issues of "nedarim" b/c after all, "nedraim holchim achar lashon b'nei adom" and the important factor is whether these other edibles are also "minei basar", irrelevant as to whether or not they are more important foods. Is this also how you understand this point?

Daniel Gray, Toronto, Canada