The changes were made for several reasons ..
When threads got moved after dropping past page 3, where did they get moved to? No idea .. so basically, after a thread got moved out of the zone, it was for the most part dead because once it gets moved, most users no longer see it and even those interested in it may forget about it or give up trying to find it.
Which threads get the most replies usually? The most controversial threads .. troll threads .. flavor of the hour threads, etc. You can't judge a thread by how many replies it has. There were a ton of really good threads that just weren't the type of threads to warrant replies. Those threads were forever doomed to some other forum so that "Roy Williams can't catch a cold" threads could stay in the main forum for days.
A lot of users have been complaining to several of the moderators lately about having a hard time finding the important Cowboys related news, discussions, etc. along with previous discussions they were participating in because they can't check the site every hour like some of us can.
There are many more reasons for this change but the overall results will definitely be much better than what we had.