Before Maya came out Softimage was the be all end all of commercial 3D apps.  Back then Electric Image, Lightwave and Houdini were the only other commercial apps that really mattered.  Then Maya and 3DS MAX came in and shook things up.  MAXXON C4D slowly climbed into a strong position as well.

Anyway, Autodesk is gaining a pretty monopolistic advantage in the high-end 3D world but there is so much competition at the consumer level I'm not too worried about it. Aside from the many consumer level commercial apps there is also an ever growing cadre of open source 3D apps to choose from.  As for them buying Carrara, or more likely DAZ, I don't think it would be a very good fit for them from a corporate culture perspective.  They would probably go after Vue or something similar that would be easy for them to digest into their their parent company. But I understand your concern. Autodesk does not have a very good reputation for making the software they buy better.  They seem to be buying up their competition for the purpose of stopping development so they can use the existing software as a chash machine.