Your post will be googled, linked and repeated, without the original link, and will therefore gain perceived veracity.
As will most of the posts on tbb, including yours and the one I linked to- you shouldn't necessarily believe everything you read on the internet
Without reasonably authoratitive links almost everything on bbs's like this is someone's opinion, but in this case I think it more likely that BT will charge for the 80Mbps upgrade than they are to give it away for free.
Where the independent ISPs are concerned anyway, Infinity may be a different matter.