This is slightly related to question http://mathoverflow.net/questions/33366/the-unprecedented-success-of-the-intersection-operator .
Apart from a set of maths books of null measure, most have the following property:
Objects definitions are presented as a conjunction of properties.
Most axiomatic are also clearly conjunctive in their presentation.
It is uncommon to have say "By definition a Zorglub is a red zorg or a white zorg".
Q1 : Do you agree with the bias (if not, give enough examples)?.
Q2: Is this bias mainly a discourse convention or does it lie deeper (where?) ?