Haven't really pondered on it.
Tell me, do you think that you or anyone else would be able to accomplish a whole lot else in life without a steady supply of food and water?
I think its relatively legitimate as theories or conceptualisations go, in fact I've been thinking more lately that some sort of reductive or simplification of theories is necessary to understand some of them clearly or accurately (?), for instance if you consider Maslow as you have here it makes perfect sense.
I like to see how certain apparently water tight or obvious theories can be critiqued though, not in a sort of navel gazing or for the badness sort of way like some deconstructionism or post-modernism, that's all bullshit, but sometimes indepth questioning or analysis of received wisdom is a good idea. It doesnt mean the received wisdom will not be found to be wise or perrenial in any case though just because it is questioned.
The thing about sex is whether or not it should be placed as a fundamental need or not, like water, food, shelter, people can live for a long time without sex, they can choose to abstain or abstain simply because they dont have that option, they could be asexual, they could see it as an obsticle in the way of enlightenment or physical or spiritual goals. That would seem to be a fair but minor criticism of Maslow's theory.
The fact that individuals pyramids differ, under the influences of culture or other factors, and its hard to generalise does not mean its not a good idea to have the theory or theorise at all though.