In my recent experience, I think the mammogram machines are getting more sensitive and therefore there are more repeats, ultrasounds, biopsies that are routinely performed. Not that this is bad but it is scary.
I had two mammograms plus two ultrasounds this summer and was in the room for the biopsy when the radiologist looked at everything and said you know this is really borderline and why dont you just do a repeat ultrasound in a few months. I was talking to my sister and she had the same experience in another town but she had the biopsy which was negative.