Ordinary TV watching people have a much broader mental scope -- spanning the globe than their ancestors did. They do better on IQ tests. The TV shows they watch are more complex than the Vauderville shows of old.
Today's Discovery Channel (and History Channel, and TLC, etc) - are vastly different than what they were when they started. All have definitely "dumbed down" to the LCD.
I understand that this is normal change for a business, especially one centered around TV entertainment. I also know that even in their prime, these channels were never as educational as, say, PBS and the like. But compared to today's programming, their earlier incarnation was vastly superior.
But that is just my (probably biased) opinion...
While with "educational" channels it.comes off as dumbing down, there's a broader effect of appealing to narrow groups that drive popularity and then moving on to appeal to the masses. Outside of TLC/Discovery/History you can see this in Food Network (where the cooking slowly migrated to the Cooking Channel -- typically on more expensive cable tiers) while Food Network was taken over by food tourism shows, advertorial series, and reality/competition shows; MTV, where the music keot migrating to subordinate channels while the main channel was taken over by non-music reality/competition programming, and lots of other outlets.
There is some choice but how many re-runs of Discovery channel content can you watch (and most of that is infotainment, not actual stuff you'd want to learn).
The one great thing about the internet is that it is many-to-many rather than one-to-many in it's foundations so we do have a lot more choice than on TV and that university is there as long as you want to look for it.