It seems that the issue has less to do with the cloud than it does interoperability (IMO). Yes, you're using a cloud service, but you could just as easily have two non-cloud services not talk to each other properly.

Tasks is something that Google hasn't done well in general. They have their own tasks system that's kind of sloppy, and I don't know why they don't support the tasks part of the CalDAV standard, but they don't.