I don't necessarily agree with the practice, but the argument I've heard is that if you only want people with a Bachelor's or higher, you have to say that you want a Master's.
What do you think the reason for that is? That those people without a bachelor's degree will be really discouraged from applying if you state that a master's is required?
Probably because, so often, it really doesn't mean anything. This phrase is usually put there by HR departments; most hiring managers couldn't care less about an applicant's (lack of formal) education if the person can actually do the work, which, in computer science, is a lot of people with no degrees.
