That isn't what happens at all.
Threads that get locked are (hey, I found xxx funny, so let me post it). Threads that have a new subject and incorporate a funny video (ex. If I made a thread about Four Loko, typed out a couple sentences, and then had the CollegeHumor Four Loko ad) are always kept open.
This is an example of a thread that would be locked:
http://bucketguild.com/phpbb2/viewtopic.php?t=9134
This is a thread that both adds something to the board and also uses videos that could go into one sticky and has thus remained unlocked:
http://bucketguild.com/phpbb2/viewtopic.php?t=9062
EDIT: I'd vote for allowing funny videos to have their own thread
IF AND ONLY IF THEY'RE GIVEN A SUBFORUM FOR FUNNY VIDEOS ONLY.
Look at how many posts are made per day in the sticky, then make each and every one of those new threads. FUBU moves by fast enough (I think an unbumped thread has something like a 4-8 hour life on the first page).