I agree with Diamond Girl. People make up rules to control others and, maybe even, protect themselves.
There is certainly a possibility that women are not permitted in some spaces of holy worship. However, giving or insinuating that the cause for such a rule is the women's weakness or "dirtiness" is not logical (as very well presented by previous posts).
It seems more likely that the rules are applied as a protection against women. Pure Dharma hold women with high esteem. For example: Samding Dorje Phagmo is a lady incarnaton with high ranking, after the Dalai Lama and Panchen Lama. She is considered an emanation of the beautiful Vajrayogini!
As information and knowledge is made accessible to more people, obsolete rules like this will be forced to disappear.