Well from what I heard Justice League and Teen Titans were originally only going to be 52 episodes but both got extended runs. JL's was asked to expand to the roster a bit and put Supergirl in it but they decided to make a whole new sort of different show entirely with JLU and Teen Titans was defintely asked for another season after the 4th which was suppose to be the last and I don't know if they were asked to change anything but probably were thus why the fifth season is different then the other four. Also as others have pointed out, BTAS, Animaniacs and Tiny Toon Adventures came out when cartoon 65 day syndication was really popular so that would explain there longer running time and the shows just wound up becoming more popular they were able to expand a bit more. The Batman is the only oddity of that since it wasn't that popular but I guess Kids WB wanted to squeeze as much from it as they could since around that time they were shutting down and knew the next Batman show would just be CN only. Yeah, 52 half hours is the standard for WB animation shows. To my knowledge, only Batman: The Animated Series, Animaniacs, Tiny Toon Adventures, Teen Titans, and The Batman have bucked this trend (depending on whether or not you count the two Justice League shows as the same)
Still yeah MAD was cancelled. The Upfront just came out and it was not announced as a returning show and it's been documented by various sources the show is done. Heck even the last episode acknowledges this in their own sort of self aware tone noting other shows like Adventure Time and the upcoming (at the time they were writing it anyway) Steven Universe were still airing on CN even though they weren't. So yeah MAD is done which is a shame as I did quite like it. I appreciate that unlike Robot Chicken they were trying to be current and relevant and continously going after different things to mock and lampoon and really yeah that could make a lot of their material rather dated but I akin it to South Park: if you watched it then the joke is really funny but even without that hindsight ti could still be entertaining. Still yeah it wasn't pulling in terribly huge ratings or anything so I can see why it only got it's overall 52/103 (as the 100th was a two parter) eps. I would like to see it on the air more but eh CN lately is lousy on letting shows that finished up air again besides for some of the most popular and well known shows. Besides at least this isn't the CN of yesteryear that had a specific cap of how many episodes you could have only a few shows managed to break and even then there was another slightly larger cap and if still popular and the like can go for as long as they want.
Man now I"m up to 7,000+ posts. Hard to believe it took me 8 something years to get that many. How long will it take me to get another thousand? Guess you're going to have to keep reading what I have to say to find out.... I hope you've been doing that anyway as I feed off the attention.