I would agree that many children with ADHD (or ADD) prefer to learn by watching or doing, and that many of these kids prefer activity-based, hands-on activities to those that involve lectures or listening and talking. However, we also know that 30-50 percent of students with ADHD also have learning disabilities. Since a majority of learning disabilities are language-based, it's easy to understand why children with ADHD, who also have difficulty using language, prefer visual or manipulative activities.
What's very important here is that teachers understand the learning style and preference of all the children in the classroom. Some kids with ADHD have great language skills. Others have difficulty organizing their ideas and expressing them so that others can understand what they mean. Some kids with ADHD are fantastic cartoonists, but may write so poorly that even they can't read their own writing. Some students with LD can create a story and tell it with a dramatic flourish, but can't write it down in a flowing, coordinated fashion. Some students do well when they are reading scripts from a play, or poems that have a pattern, or songs that have a beat, but they can't use their own words to tell a tale.
All students who have been diagnosed with LD or ADHD have had evaluations that are supposed to determine their best learning styles. This information should be readily available to teachers. There are also many tools that teachers can use to find out how all children, not just those with identified special needs, learn best. If teachers don't use this information in planning lessons or units of instruction, they are not taking advantage of the learning strengths that each child can bring to an activity. A good teacher also knows his or her strengths and preferred style of teaching. Making a good match between the way kids learn and the way a teacher teaches is the hallmark of a skillful teacher. It's fairly easy to find ways that allow children to fail; it's an art to find ways to use their gifts to help them find success.