Bandwidth Question

I'm watching a stream that is listed as 1000 Kbps. Unless I'm mistaken, this means that the max downstream bandwidth will be 125kB/s. As I streamed, I checked my real time bandwidth usage in my router and the stream was maxing out my downstream at 620kB/s. Although there were a few dips, for the better part of 45 minutes, my downstream was maxed and I didn't have anything else running on my network at the time. Can anyone explain this?

Thanks.