With CloudKit, you can focus on your client-side app development and let iCloud eliminate the need to write server-side application logic. Cl
You cannot upload any code to run on Apple's servers?
You can and you can't. You can't upload code / SOAP based web services to the server, instead of it you can upload / store observers on the server, called subscription.
whole thing pretty limited and not really comparable?
I would say in CloudKit and in MBaas client communicates with server though a more narrower more robust interface: you can not upload exotic web service to do XML parsing, database manipulations and based on it trigger push notifications, but RestFull architecture allows you to perform the 4 basic operation on the data store, and with subscription client can get notified about INSERT / UPDATE / DELETE operations performed on tables.
I think MBaas is just the next step in evolution of server - client architecture. First it seems it is limiting, but you can do all as in SOAP based web services world. Development is extremely fast / scalable / comfortable to use and easier to control things like permissions / setup, maintain server, security needs almost no effort.