So regarding pageviews, this would be the same logic, given that anything in segment A is in segment B, this means that every pageview from each visit in segment A would also be in segment B, with any additional pageviews from visits that are in segment B.
Meaning that in theory the number of pageviews in segment B (OR statment) should always be higher than segment A (AND statement).
This is all based on the hypothesis that anything in segment A, is also in segment B- you could test this by creating a venn diagram visualisation using both segments- if the circle representing segment A is entirely contained in segment B, then we can confirm this to be correct, otherwise there may be some piece of logic in either segment or in your tagging that's resulting in something strange going on.
It'll depend on the site, but in theory, I'd assume you're correct in most instances because of the following;
This is assuming the site is a basic eCommerce site;
You could add a product to the basket from the product display page (This session now qualifies in segment B as I have viewed the product page)
You then abandon the site, returning an hour later in a new session. In this new session, you go ahead and complete the basket transaction (Again, this session qualifies in segment B as I am now purchasing this product)
In the above scenario, I have 2 visits in the "OR" segment (segment B), neither of which fall into the "AND" segment (segment A), as a result, segment B in theory should always be higher than segment A.
Any visit that falls into segment A, should also fall into segment B, as well as the above instances, which won't fall into segment A.