Women definitely have a lower center of gravity than men; that is a proven point demonstrated in the structure of their hips and in how they carry and distribute their body weight. Look at these pages for some quick information:
...otherwise, just google up "men women center of gravity" and you'll see several sites dealing with allowances/changes that must be made in different activities because of this discrepancy in frame between men and women.
Secondly, on the emerging topic of center of gravity vs. hara, in so far as one is encouraged to move from center (hara) and as aikido tends to be an art that maximizes the body's potential through proper mechanical application of the body and limbs, the two concepts of "center of gravity" and "hara" reference the same point in the body. There may be more spiritual, holistic appliations to the concept of hara and how it interacts with shakras, etc., but there can be no doubt that the points are one in the same: to move efficiently and powerfully (the mechanical goal of aikido), the center of gravity must be manipulated. The situation is easily demonstrable through the application of modern physics and physiology. Even inanimate objects are most easily moved through an understanding of their center of gravity.
Any misunderstanding of hara (specifically the tanden) and the center of gravity as two separate points in the body fails to explain adequately the biological proximity in the mid to lower pelvis of a human. There is single point in the hip/pelvis area which has significant mechanical meaning. Any discussion of the points as being separate seems to me to be a retroactive definition caused by an incomplete knowledge of women's physiology (e.g., that they have a higher center of gravity).
JMO, of course.
Finally, I agree with Tonya, Jon. That comment was completely inappropriate and juvenile. Find a chat room.