Hmmm, well I'd point out that you guys are missing an important point. A lot of the changes to these shows doubtlessly happen because YOU (adults) like the shows. It's an intentional security matter.
Originally there was a lot to be said for children's shows that could also appeal to an adult audience, Anime, especially when it picked up through the 90s got a lot of attention that way (when people pay $30 for a subtitled VHS producers take notice) and inspired the design of a lot of cartoon shows in the US. This lead to a lot of pretty popular properties being developed, and lead to a lot of money being spent as adult fans purchused stuff for their kids (uh huh).
The problem of course here is obvious, when you create situations where random adults and children mix in the same cosm it becomes pedo-bait. Something a predator can use to chat up a child and form that all-important initial connection when the parents/guardians are not around. Sometimes watching a random 40 year old discuss [insert show here] with an 8 year old can be cute, if a bit creepy, but othertimes it's hardly harmless, and people DO keep track of the techniques used by child predators.
Business started to adapt to this, official or otherwise. One thing you'll notice with video arcades at locations that still have them, especially BIG locations is that they are increasingly getting rid of video games that can be justified as appealing to a more adult audience, or having a long-time fan base. People had been trying to ban violent games for years without success, but now your seeing something similar voluntarily, generally when places that have become security conscious, or have otherwise had an "incident" in their past (molestation, or a near miss) not having those games makes it so creepy adults don't have an excuse to hang out in arcades, popping in an occasional corner, and watching the kids, looking for oppertunities.
Back when I worked casino security there was a dance over this with "decent" cross-age machines waffling back and forth based on security concerns and what was making money. It should also be noted that adults wearing mechandise or logos for populat children's television shows warrent special attention, someone to keep an eye on, especially if they gravitate towards places where kids are left unattended (which should never happen, but does anyway). There are exceptions of course, popular super heroes like Marvel and DC characters for example, but basically if you see a 40 year old due wearing a My Little Pony T-shirt trying to chat up little girls in a video arcade, that's not a good thing.
At any rate given all the back and forth about this kind of issue, I suspect the number of children's shows going "old school" and aiming for a child-only audience, removing a lot of the depth, referances, and humor that would attract adult fans is intentional. We're not talking about the kinds of trends you make laws about, but basically nobody wants to have their product lumped in on semi-official security/police watch lists or become known for being used as pedo bait.
I'm not saying this is definatly the reasons, or the only reasons, just that it's an angle you might want to think of because it's come up before when I worked security. One of those things where you know "we can't officially tell you some dude wearing a Spongebob or Invader Zim T-shirt is a creep, but in context if you see someone wearing one around the arcade, that's one of the guys you probably want to keep a paticular eye on... along with everyone else in general of course". The point basically being that anything that can be used to form a bridge to a child, get short term trust, or act as a lure can become a risk, and pedos are VERY good at it. "I'm not a stranger, we both like My Little Pony, and look I've got episodes that play right here on my kindle, let's head over into that stairwell where it's quiet and you can hear and I'll show you a couple of episodes you probably haven't seen yet..."
