Where are most JAV movies watched today: on a large screen TV, laptop monitor, or small screen handheld device? If there's been a change in emphasis, maybe that has influenced it.
Related idea: most people expect maybe a decade-long downturn in the global economy. I wonder historically how porn as an industry performs during hard times? (too many puns to avoid them all) Certainly it would not be a time to invest in new equipment, or expect your customers to.
(1) I don't have a good answer, but the more meaningful question isn't most WATCHED, but most paid for. The studio have to get paid in order to film and distribute AV right? A trend I notice in general is the slow disappearance of HOME PC and even laptops. Phones and tablets are getting a lot of the jobs done and at home, TV's on their own or TV set-top boxes are getting so smart to blur the line between cable boxes and PC. But that doesn't even matter that much. High Def (even 4K) tablet is getting common and 4K smartphones. And both big screen TV and PC are commonly supporting 4K resolution. So it all doesn't impact the HD vs. SD question. I suspect the surprising staying power of SD in AV is due to the staying power of DVD.
Or perhaps... most guys just don't really need HD for whack off. I prefers HD but SD does the job well enough.
(2) Historically (mildly) bad economy is good for home entertainment. Because people or family who's hurting in the pocket books may use their limited budget on a big screen TV or high tech game console which last for 5-10 years and satisfy them instead of yearly vacations or weekly dinning out. Or every 3 months they can afford a new game (US$60?) which is good for several family members and even friends for maybe 100 hours, but that $60 maybe not even cover one evening of dinning and entertainment out side of home.
For AV, I imagine bad econ will really hurt dating and getting married (and even having kids) and of course it's very bad for hosting, delivery health, or plain prostituting. So you have a lot of guys with time on their hand, a little bit of money, not enough for REAL fun (involving women) so they may spend it on renting or buying AV. Of course if the econ get so so bad they can't even afford 1 or 2 rentals a week (let's say a typical wanker needs a relief every day but consumes only one scene to do the job so each DVD is good for 3-4 nights, that means 2 DVD rentals a week). Of course a good customer rents 7 vids a week.