There are many reasons why a post might be passworded, most of the reasons in the past have had nothing to do with current 'practice'.
Just because a post IS passworded doesn't automatically mean 'bad'. Especially when the password is publicly INCLUDED at the time of it's release, i.e., no silly 'go to this website' nonsense and the like.
The biggest reason is that passwording prevents/eliminates 'man in the middle' type 'attacks', where dodgy code (read: virus) or other nasties can be inserted in the middle of an nzb, causing it to be downloaded along with what was originally intended.
When the d/l'er runs an unrar (on a passworded rar), those 'added' parts simply won't be processed. If it isn't password protected, THEY ARE.
Now, as it comes to hdvisuals, for quite a while there they were NOT doing this, and were posting a goodly amount of BD25 sized stuff. (I think the last I got was the new 'Alice In Wonderland'). Then all of a sudden, this rash of encrypted. Don't know why, and there is no clue (directly) in the nfo, nzb, or otherwise.
Now, there was a technique used by some in the very early days of HD stuff, that included a password keyfile in the parity (par) file, that would 'magically' be restored when the rar was 'repaired', since it was never actually posted.
I haven't tried that on any of these new postings, and maybe I'll assume that you ran quickpar on these files, even if it looked like they were 100% (but quickpar would report even then that one file was missing).
Don't know.