"Just to be absolutely clear, you are doing 'Right Click, Get Info, Open With, Change All'?"
Yes, that's precisely what I did.
And, yes - I expected it to open with whatever program I specified - just as Explorer will do in Windows or Nautilus in Ubuntu. My comments resulted from my surprise that I was unable to set AVIs to open with VLC despite my numerous attempts.
And I apologize that I wasn't very clear. I was pretty limited time-wise and didn't remember the exact wording or process. However, I know I did "right click, get info, open with, change all" since that's pretty much the same way it works in Windows - and the same way I set MKVs to play in VLC earlier - on the same machine.
But I think another Slashdot reader has posted the solution:
"I believe you're running into a "feature" that's causing some confusion. If you manually change a document's open with application it segregates itself from the pool of documents that change when you hit "change all" on other documents. In case it's 12:30 and I'm not making sense I'll give an example...
You have a.tif, b.tif, and c.tif. The default program for opening .tif files is Preview and all three files in question are opening with the default. You change a.tif to open with Photoshop. You then change b.tif to open with Firefox and hit the "change all" button. You'd then be left with b and c.tif opening in Firefox, and a.tif opening in Photoshop because you changed it manually from the default. At some point in the future hitting change all on a.tif will both return it to the default pool along with b and c and change the default .tif program to whatever a.tif is set to at that moment.
I think for one reason or another these avi files think they're all out of the pool. You can change the files already on your drive to use the default quickly by using the Find command to find all files ending in .avi on the computer, then hitting select all and then command-option-i to bring up the inspector. Then change them to open with the program of your choice and hit change all.
Hope this helps, works, makes sense, and wasn't too wordy (I don't know how well you know your way around the MacOS so I explained a bit more than usual)."