I think it is important to distinguish between "official" definitions
of words like "museum," concocted by organizations to fulfill
eligibility requirements (i.e., ad hoc definitions designed to fill a
specific need) vs. dictionary definitions, which are intended to be
universally accessible to the speaking masses of the language. Anyone
ought to be able to look up "museum" in any dictionary without having to
consult AAM or any "professional" body to get the latest twist or "spin"
on the word. The AAM emphasis on "non-profit," for example, is a
logical, defensible requirement for its purposes: they have every right
to include this in a working definition, and I'm sure that this sense
has been included in some up-to-date dictionaries, IN ADDITION to the
earlier, non-fiscal concept.
  But I don't think it necessarily follows that this constitutes an
alteration in the basic definition. For example, I think it's an awkward
(and arrogant) mistake to impose a "non-profit" requirement on all
museums, excluding corporate museums from "museum" status. I find it
easier to think in terms of profit-making vs. non-profit museums than to
have to invent a new word for either a non-public or a profit-making
museum. Many people want to redefine words based on personal or popular
value judgments--and peripheral features--rather than essentials.

An interesting redefinition argument which I have run across involves
photographers who feel that amateur photographers should be excluded
from the definition of "photographer" because only a person who has made
a commitment to earning a living in the profession deserves the title.
Again, this represents an attempt by someone with a personal,
professional, or social agenda to impose a new definition on a word. The
inevitable result is confusion and miscommunication. I suggest leaving
language in the care of professionals. --David Haberstich