Well the bottom line I feel is that LOTS of games are educational without INTENDING to be. When a game is specifically built around teaching a specific thing though, gameplay becomes secondary to the actual educational lesson, which makes many of those games less enjoyable.
You take games like Civilization, Minecraft, even Assassin's Creed and there's educational value there without compromising gameplay integrity. As a teenager, trying to understand the intricacies of how to maximize my characters in an RPG taught me way more about algebra than any school textbook did.
I think when education is an overt thing, it makes it less enjoyable experience because it's marketed as an "educational tool" and lacks anything beyond the most basic elements required to teach and interact.
In Minecraft I can learn about spatial relationships, architecture, even basic mechanics.
In Assassins Creed and Civilization I can pick up little interesting tidbits of actual real world history.
In Scribblenauts I can learn a lot about problem solving, proper spelling, and even the value of adjectives.
There's all kinds of games that also sharpen our senses and our analytical abilities. In my mind MOST games are educational at some basic level, but when you prefix one as an "educational game" you're basically telling the audience that the game's purpose is education, not enjoyment, and while YES you can enjoy Oregon Trail or Carmen Sandiego, or even Mario Teaches Typing, they certainly are somewhat lacking in comparison to games built specifically around being FUN.
