I'd be interested to see studies emerge on the value of entertainment in educational content as the child ages.
In my direct experience with my own children, entertainment provides value due to engagement as mentioned in the article. But, entertainment switches from engagement to distraction around age 5 or so.
My 2 year old definitely stays more engaged with the alphabet app and basic counting apps when they are entertaining.
However, entertainment is highly distracting to my 6 year old.
I've found at 6 she's more interested in how the learning actually applies to the real world, so she engages with educational apps as a means to an end. For example, she likes to write stories. So, she asked me to download spelling apps so that's its easier for mom and dad to read her stories.
With all of that said, I'm a huge believer in the potential of technology to improve education. IMHO, education is no where near optimal.