If pictures of the topic offended them, why were they on the topic in the first place? If you don't want to see pictures of vaginas, maybe you shouldn't look up vaginas?
Indeed. Because clearly there is no better way of teaching someone biology* than to simply show them a bunch of pictures of different people's vaginas. </sarcasm>
The main problem is that even though medical illustrations are both prevalent and often better at highlighting small details (artists can control contrast of areas very easily to show off such details), there are many exhibitionists out there who add self-made images just because they can. Most people don't post these images for their encyclopaedic value, they post them so that there's a picture of their penis (etc.) on a popular public website. The end result is an article with 10-15 different photos of the same body part, when 1 is sufficient.
* Note: whether or not Wikipedia is the best place to learn about a subject such as biology is a different argument altogether. But as long as one is careful with references, there is no question Wikipedia offers a lot of useful, factual information.