Well, if it's so difficult to implement that it happens to a great number of developers, I'd say it's an iCloud issue.

Not necessarily. Sync--particularly sync which can involve changes at the same time by different devices--is hard. A lot of devs just don't want to fully implement the required mechanisms.

I agree that sync is hard and I wouldn't even blame iCloud since it's rather complicated matter, but there are three things that made me do so:

1) They made it a de facto standard and showed developers how easy it is to use when seemingly, it's not

2) iCloud even messes up simple sync tasks, like: buy a new device 3 out of 5 apps won't start after a simple download from iCloud

3) The problems occur to so many customers and developers that Apple should communicate the problem with developers and adapt their approval system.

Sync is not that hard. I have never had a problem with Dropbox, for example, and that was made by brogrammers.