The post is triggered by the recent leak of celebrity nude photos. Apple has claimed that the iCloud ecosystem is secure and the leak was the result of targeted attempts. Nevertheless, they eventually decided to tighten the security of the ecosystem. This is not an isolated incident as I clearly recall a previous incident involving social engineering to trigger a password reset. The hacker then went on to use the "Find my iDevice" feature to systematically erase the victim's iPhone, iPad, iMac, completely cutting him off the internet.
Having all of your devices and data stored on a single ecosystem is very risky. The provider might have implemented multiple security features including 2FA but at the end of the day, the weakest link is still the user, who can be social engineered into revealing whatever privileged information required. Financial advisors have long been preaching the message of not "putting all your eggs into one basket" but the idea has not really caught on in consumer IT.
One of the biggest benefits of a single ecosystem is the syncing of data across devices seamlessly without any user intervention. However, this gives rise to yet another problem. Most users have no idea how much information is being synced and where it is stored since it is all done automatically. For example, Mary Winstead claims that the leaked photos were deleted a long time ago. Few people knew that Apple kept 3 backup images just in case the most recent backup image is corrupted. Backing up your data manually might require a bit of technical knowledge but it gives you much more assurance about the security of your data.
Lastly, there is an inherent risk with storing data on the cloud. Data loss might occur due to mistakes made by employees or the company itself might even cease to exist. I do use the cloud to store my data but my mantra is "Store only what you can afford to lose". I always keep my most private data off the cloud and on my own HDD.
Edit: It has happened. Files were lost due to a bug in Dropbox's selective sync feature.