The Max Hardcore videos are some of the best selling porn videos.
Max is the extreme of the extreme and was even jailed for a couple of years for his obscene works. I would question your claim of him being one of the biggest sellers? He is despised in the industry, he is despised by porn lovers, his stuff is banned from many sites and forums. You will not find his works hosted on many sites at all. It's funny how he always seems to get wheeled out in these kind of discussions, i expect half of his web traffic is generated from mumsnetters using his website for 'research purposes' 
also you say hundreds of thousands of views, to put things in perspective we were looking at 15 million views for that 'Next door Nikki' softcore site i mentioned earlier.
Have you actually read the study you linked to?
It clearly states in the abstract (on page 3) why they chose to analyse video rentals;
Although consumers access pornographic materials in a number of forms?including the Internet, cable and hotel video-on-demand, the telephone, and magazines?videotapes (VHS) and digital video discs (DVD) still generate the most income (AVN, 2006). In fact, rentals at adult video stores increased from US$75 million in 1986 to US$665 million just 10 years later (Stack et al., 2004), culminating in over 950 million adult videos rented annually by 2005 (AVN, 2006). Video rentals generated more than US$4.28billion in 2005, representing 34% of the total market for all adult products (AVN, 2006).
And do you know what that AVN is?
Yes, yes and er yes. Ok here we go:
a) Have you verified the accuracy of that AVN chart?, as all i am finding is that people are claiming it to be based on the number of adverts for a particular product not actual sales. Also that $ 4 billion figure has been disputed too as being massively inflated and when they challenged AVN they were a tad vague. Check Wiki (AVN magazine) and look at the history section. It's all there and it appears to be very dubious.
b) So they claim 34% of money is made from DVD products alone, but why didn't they consider the other mediums of the remaining 66%?
c) How many people actually go to a sex shop and buy porn or order it through the post, when it's all free on the internet? Do you really think that there are many people who go to this trouble? I'd estimate it to be only small percentage of people who still buy porn. It may generates a fair amount of profit but is still a niche market in the grand scheme of things. They are basically the equivalent of people who still buy music on vinyl.
So from that i would strongly disagree that the study uses a solid method. It's what i would term junk science