You know, until this year I had never owned pumps -- not a true, slip-on, strap-free pair, anyway. I owned several of pairs of almost-pumps, but all of them had some kind of maryjane strap. These were what I used for dressy shoes.
Then this past spring I was captivated by a pair of floral pumps, and bought them. I ended up returning them because, colour-wise, they didn't go with very much in my wardrobe, but in the process of trying them on with everything I own, this is what I discovered:
1. They make my legs look like they go on forever. This is quite a big deal since I'm only 5'1"!
2. They are a match made in heaven with midi skirts. I'm really into the midi at the moment, but I was struggling to style them so I don't look short. Pumps are the best (although not the only) answer to that problem.
3. They look great with skinny jeans, whereas high heeled shoes with a strap do not. Skinny jeans with pumps is my new favourite going-out-for-the-evening formula.
4. They feel classy and professional. If I needed to attend an interview, they are just the thing.
I ended up exchanging them for classic black ones, and then liked them so much I went back and got olive ones too (which are now on sale, btw):
http://www.fluevog.com/code/?w.....ourID=3242
Part of the reason I like these so much is the elegant, slightly retro cut and the wider heel, which to my eye looks more balanced. I'm not a big fan of stilettos, and the wider heel is more walkable anyway. Also these are very comfortable for a 3" heel.
So. This is a sort of roundabout way of addressing your question. My final answer would have to be no, not every woman HAS to have pumps, but for me they have filled a wardrobe hole I didn't even know I had. I am utterly surprised by how much I love them. So if you really like those pumps and think you'll wear them, go for it. If you think they'll just languish in your closet, perhaps you should save your money for something else.