Life's never quite so simple as you'd think, although I don't think the nose-up attitude, if you're right, is large.
The most efficient cruise is achieved at the speed at which the specific air range (nm/tonne of fuel or whatever measure you care to use) is greatest, not at which actual fuel consumption is lowest.
So, by the time you've factored in engine efficiency, altitude, variation in L
with attitude, wind, colour of the pilots socks, etc. you just occasionally get a slightly surprising result.
For example, I was recently flight testing a slowish light aircraft perfectly content to cruise at about 85 kn, and most comfortable cruising about 75 kn. When I dropped all the numbers out I discovered a best range speed of 51 kn (giving an SAR of about 5 nm/L), whereas cruising at 75 kn (which as a pilot felt right) I got an SAR of nearer 3 nm/L - a huge reduction in range or, for a private owner whose primary cost is fuel not hours, a large increase in cost from A to B.
So, although I don't have enough experience of airliners to know if BF's facts are truly correct, they don't as presented surprise me hugely.
G