Doesn't surprise me. You have to watch every bill carefully. I recently had a hard drive (ordered on the internet) put in my computer by a local shop and a lot of other stuff done. I called ahead and asked what the bill would be and when I went to pick it up and pay, they had added over $100. I asked why since they said on the phone (can't remember exact amount) and they said you had a hard drive put in. I said I brought in my own hard drive, and they deducted it. For all the stuff I had done, I might have paid without blinking, but what was done they didn't have to monitor constantly (transfer of date).
My sister and her husband had a lot of electrical work done, and my brother-in-law went over the bill and they tried to overcharge them $2000.
Back to the subject at hand. I heard this discussed on talk radio locally, and it was claimed that it is a common practice to overbill people with insurance to cover the non-paying patients. Add that to a lot of people aren't feeling all that well and may not look at their bills too carefully.