These gargantuan rar parts (i.e., I've also seen and tried to 'process'those gigabyte plus things), is really ridiculous. A 4-core top CPU has trouble running quickpar and unrar on those things!
You're probably right about 5% vs. the 10% of years past...
But NOT the 1% or less, and I've seen that!
A few technical truths to what we're talking about, and that's digital transmission (both 'local' and 'long-haul').
ALL repeat ALL transmission, whether on fiber or copper coaxial or twisted pair, is ANALOG. We all talk about 'digital' transmission (even over full FIOS attached to terrabit internet routers). And I'm not talking about the 2-foot piece of ethernet between the home router and the computer at the end users home/office.
Folks 'think' the fiber links criss-crossing the planet are 'digital', when in reality they aren't. They're analog. Don't believe it, I can point you at some heavy-duty engineering books explaining transmission theory to you.
So... errors will happen, period. From the originator to the usenet server (where hopefully it's pretty 'safe'), from that server to the other usenet servers (the 'bucket-brigade), then from there to the end 'leech'. The entire process is, of course, only as 'strong' as it's weakest link (usually those end-user to server links, traveling across copper wire or fiber of some sort).
Most posters don't do the basics, in other words, they don't 'watch' their posts from another usenet server that ISN'T the one they are posting to. Example: Post to Giganews, watch the propagation at Astraweb.
I think the traffic that the HD stuff in generating is being posted by folks 'new' to usenet. I can't otherwise figure out why a ton of it is being 'stripped down' from 45G to 40G by stripping out things like commentary tracks, foreign language captions, and other things that save at best 1/10th of the upload time. This kind of wackiness, I thought, had went out a LONG time ago with stripping out DVD5's, but I guess with increased bandwidth didn't come increased smarts.
Along the same lines is, why the decreased pars...? Well, I think that a lot of the folks doing that, from the speed of the uploading, are on FIOS or some other super-duper-speed system, and have either forgotten or never had to deal with the 'real world'. Again, at the speed of the posting, we're talking about the 'thin edge of the wedge' time wise to post more.
Oh well, there are a lot of good posters out there doing mkv stuff, and a few doing full BD posts. But the BD folks are being drowned by the wacko's to the 'strip' jobs. At least they're admitting to it in the nfo's, so one is forewarned before spending x minutes/hours/days.