It was a bit of a case of "we can't please everyone". iCloud was investigated, but due to some early decisions made when the app was first developed (before iCloud existed), there was significant work involved in making Posted work with iCloud (basically converting the database technology). 

In addition, choosing iCloud would close off the possibility of ever doing an Android or web-based system and using the same synching platform. A web-based system is already available for Posted, this would not have been possible if iCloud was used.

Facebook and Twitter were also looked at, and the first version of sync was using Facebook for authentication. But then there were way too many complaints from anti-Facebook people. 

So in the end, a custom account seemed the only way to not introduce barriers for people. It is a simple and free sign up process. And once setup, you will barely have any knowledge that the account is running in the background.

Done