You missed the point!!!!! You do not need 40mbps for stellar PQ. All the top tier bluray releases are at 24mbps AVC. Spiderman pick a number, Pirates pick a number, Casino Royale, etc.
Your point is moot. Average bit-rate isn't the key issue here: Peak-bit-rate is also important for high-action scenes and most every BD I own from Disney shows video bit-rates that routinely peak above HD DVD's limit.
And besides the simple issue of video max-bit-rate, there's the whole spectrum of signals that share the read-bandwidth. Blu-ray Disc is much better able to deliver optimal video *and* lossless audio and additional features like PIP that all need to share the same bandwidth pipe. It's not just about video rates, it's about the interaction of every signal that needs to share the bandwidth space.