Jno, the phrase that leapt out at me from your link was "creative accounting."
Also "There's no way of testing if what they're saying is really true."
I believe it would be difficult to ascertain just how many extra tourists were in London (a very popular tourist destination year in, year out) primarily for the games.
There may have been a temporary 'feel good' factor, up here in Burnley, while the games were taking place but i don't believe it added anything to our town's economy, employment figures, etc.