Actually, it seems not all songs are recorded at the same bit rate. Checking through my library 2Pac's 'Me Against the World' plays at 834 kbps while 'California Love', which is off of the same CD, plays at 1.04 Mbps.
But 900 kbps is a rough average.
It is important not to confuse the bitrate for lossy encodings such as MP3 with the file size differences of lossless compression. The lossless bitrate for 16/44.1 stereo is constant at 1.411Mb/s; it is the file size that varies due to "zipping". It is just more convenient for the onscreen presentation to use the "bitrate" field inplace of "compression ratio" to avoid use two columns.
