I do not want to start a debate about ECVs as this topic has been more than thoroughly covered in other forums. However, I do have one observation to make. The reason you do not see ECV's in the other Disney parks is because the USA, to a large extent, is handicapped friendly while most other places are not... Elsewhere, even in " touristy" attractions and cities, if you are not able to get around on your own two feet, you are mostly out of luck, I guess if you are handicapped or old you are supposed to stay home..
EDIT. The problems are transportation, curbs, door sills, steps and stairs.