I think this would be a valid question to ask lesbians too... vaginas come in different shapes, sizes, textures, muscles tone and activities levels, not to mention smells and the fluids which lubricate them have different qualities and they change over time and with experiences.
Non-penised, hetero person here, but having hung out with a bunch of midwives and having stalked fertility forums for many years, I believe it's not that vaginas are differently shaped, but that the position of the cervix can be wildly different (and change thruout the month)