This is wrong. I am a consultant for a major consulting firm and I have worked at three different client locations this year. I don't know where this idea of limited mobility comes from. Sure there are some restriction but they aren't as bad you have made them sound like.
There is no difference between working for one company and providing services to three different clients and working for three different companies. The paperwork is the same. Every time they have to file an amendment.
I have changed jobs on this visa as well. It works the same way.
