Lego's robotics stuff might be patented but their core brick isn't anymore. However the generic replacements like Mega Bloks just don't snap together nearly as well as LEGO. For a toddler making a little garden out of a few blocks it's fine, but you can easily make a vertical Duplo stack that's 3 times taller than the maximum stack you can make with Mega Bloks, and that kind of structural integrity becomes very important in robotics.