"I think that firstly, there is no way a woman would get promoted to the same senior roles if they were never out of jeans, and also that there are no women wearing a suit everyday because of the negative associations of women in business dress that exist in the department."
I think it depends on the job. We can wear mart casual clothes to work. so we can wear smart jeans and shoes/boots - not ripped jeans and trainers/canvas shoes. There is a girl in our office who always wears scruffy jeans and scruffy shoes. She looks like she doesn't care or want to progress, and she always gets overlooked for management roles.
She is perfectly capable, but unfortunately you not only have to care, you have to look like you care.
No female I see nowadays wears a suit to work. If they are smartly dressed it is always a dress or a skirt and blouse/smart top.
I think the advice you have been given here is excellent and it is a good idea to dress like you look like you want the job.
I am no fashion icon, but do want to look nice. I'll be honest and admit that I don't understand why anyone - male or female, is so disinterested in what they wear.
There are some great "good grooming" threads on here as well, and basically the consensus is usually a good haircut, clean hair, clean and tidy nails (they don't need to have polish on, but just look manicured), tidy eyebrows and clean and tidy clothes.