Lehninger runs the numbers for dG like it's a coupled reaction. I was confused by this, since I was under the impression that pyrophosphatase was a free enzyme. I asked my biochem prof whether pyrophosphatase interacted with the enzymes "using" the energy from the pyrophosphate hydrolysis so that the reactions could be coupled, since there wasn't any mention of this in Lehninger. Her reply was that she wasn't aware of any literature supporting any such interaction, and that LeChatlier's was how she saw the hydrolysis carrying the reaction.
A reaction doesn't have to be favorable to run to a significant extent or even completion if that reaction is irreversible (which rapid pyrophosphate hydrolysis would lead to).
That said, it's possible she's wrong too. She answered on the spot - didn't pull references or anything. And Lehninger gives the opposite impression.