Maybe the distinction isn't necessary, but David is talking about *average*, or total bitrate.
The Blu-Ray spec allows for:
Max video bitrate: 40 Mbit/s
Max total bitrate: 50 Mbit/s
Max data transfer rate: 54 Mbit/s
Lots of BDs will spike over 50 Mbit/s. BD standalones have to buffer the data.
Below is how Master and Commander looks in BitrateViewer. Not a very high average bitrate (under 28), but look at peak bitrate: