That drawback rule existed at a certain time, I am not sure if it did from the 1780's to mid-19th century. I think really what the quotation was saying as Ron Pattinson explained was that the beers were stronger than the brewers wanted them to be, in this later period anyway. I still think they would have been fermented out on the trip over and the net effect therefore was stilll a dry beer but probably over 6% ABV instead of weaker as brewers wanted. They did not want it too strong because the hot climate of export markets generally called for a medium-strength beer. (One of the many research findings Ron Pattinson has made is that IPA was not always or typically a high-strength brew).
The Fuller's IPA recently available in Toronto is fairly dry in taste, possibly less attenuated than some 1800's examples, hard to say, but very good. I had some from two casks, one at Volo, one at Twisted Kilt, and both were excellent but slightly different as one would expect of real ale. The St. Andre Barley Juice by the way at Volo recently struck me as a beer in this stronger IPA style, very well-hopped and not too malty. It was excellent, an excellent interpretation of the style in my opinion.