Well, always I'm telling my friends that I want to get a Mindstorms set for building LEGO robots/devices, I get responses like "do it yourself" and "just add controllers and some motors". Well, if it were that easy, I'd surely be in for having my own robotics set. Mindstorms isn't just a controller you can glue on your LEGO bricks. It's a system of sensors controlled and read by a single chip or multiple ones. You don't just try to fumble with some electronic parts and big plastic bricks. You don't need to build connector pieces, you need to create nicely integrating motors/sensors, it has all the ways to communicate with it's system parts built-in. It#s a complete interface built around LEGO parts and programmable with almost everything you can image. There are even Linux operating system for it, so you can -theoretically- port programs to it with enough adjustments. I can even take my code base and continue programming on it with no effort, just using another library for accessing connected sensors. So anybody telling me it's easy to build your own complete Mindstorms system with all these features should totally show it to me. And if so, it's sure nobody can archieve this without knowledge in electronics and such stuff. I pay for the comfort and they easyness, not only for the function. If I would create own kind of Mindstorms chip, it would take years for me to a) learn all the stuff and b) some more ages to actually build it with all these functions.
Mindstorms isn't just a simple set of electronics everybody without knowledge about it could create. Saying otherwise is like comparing a single CPU compared to a full computer setup with operating system.