I note that iStock is very quick to lock down threads.

Maybe they're just trying to encourage everyone to quit hanging around the forums so much and get back to work taking pictures and uploading files 

The forums can be both a great source of valuable information and opportunity to bring up important issues related to photography as well as a source of complete and utter garbage.  I suspect most people find the utter garbage sort of like looking at a bad car accident on the highway - it's hard not to look.

I've learned some really valuable information from some experienced and talented photographer on various photo forums. 

Time's up - gotta go upload.