I'm started to get tempted to upload some graphs to demonstrate what precisely I mean. I kinda wish I had all my data from our various discussions in the Toonami forum here that I had used to make points (PS I still really miss William. He was great at helping discussions along with facts!).
Here's a (bad) example I drew up quick from Google Docs:
http://goo.gl/HrdoF
Note those numbers aren't accurate, I am just making an example of what I mean.
Essentially what I mean is when you look at graphs that show the build up in viewers up to DBZ Premiers it was always a consistent climb and a consistent decline coming off of DBZ. Sure, DBZ was slamming the ratings, but its acclimation into the block made the various other ratings climb along with it so much to the point that there were peaks where Gundam Wing was actually pulling in more ratings then DBZ at points.
After you saw things like Sailormoon and Reboot leave the block, ESPECIALLY after the increase to 3 hours, those ratings become more dodgy. You'd have one show perform really well and the next show perform not as well, etc. That, to my recollection is also when Toonami was doing less cross promotion and relying too much on the block's success.
Thats rally the point I am driving home here over and over. If you have a WELL MANAGED block, you can pull in viewers to shows that might not usually watch that show. Every single person when really pushed on that point in this thread has agreed about that so far.
The thing that does tend to make this debate a little harder to illustrate is Toonami was really the only block of its kind ever. You had some good blocks in the past like Cartoon Express, Fridays amongst other ones that helped cross promote their shows, but you also have other blocks like Animation Domination that has done nothing to help or support its shows. Its "block format" is so loose that it barely uses bumpers and it barely cross promotes its shows.
Like anything though, when I talk about all these dynamics, its completely a team effort between the relationship of the Block, its shows and the synergy there in. As long as the synergy holds strong, cross marketing is easy and fun for the viewers, if shows lack synergy, then it becomes a little harder and a block really doesn't define those collection of shows well.