I relay the information about the romaine because it's what is used at the LBAOP for free feeding our tangs, a public aquarium which is neither in the business of selling fish nor killing them. Believe me, I was surprised, but it is what is used, quite copiously, restaurant grade only (as are all the foods fed to the animals). In my opinion the fact that this is a public aquarium greatly enhances the veracity of their practices.
This place is run by folks who actually have degrees, as well as sporting its own lab. We also house many, many hundreds (if not thousands--let's just say there are more than I can count) of tangs, including the fattest Powder Blues I've ever laid eyes on. Yes, terrestrial plants turn what already are into even greater poop machines, but the point is to keep them happy and FAT, yes?
Therefore, again, in my own HONEST opinion, the information garnered from such an establishment is to be highly regarded, and is not as questionable as other sources.
As for the nutritional content of romaine for humans, I do also happen to have a registered dietitian in the house (my own mother--who sports a Master's in her area of expertise) who disagrees with the assessment that romaine lacks nutritional value--it qualifies as a green, leafy vegetable.