No, in Mac OS X you can have as many levels of folders as you want. I'm not sure what the article is trying to say… In fact, Mac OS X still relies in directory structure to… well, give structure to its filesystem. We still have /usr, /Volumes, /Users, /etc, et al.
I think the article may be referring to the directory structure in iCloud, which allows only one level of nesting similar to the folders feature on iOS and in Launchpad. John Siracusa's review describes it[1]:
"Only one level of nesting is allowed, and the "folders" are of the iOS variety, complete with tiny icon previews and inline expansion of their contents."
That's similar to the AWS S3 namespace, though deeper directory structures can be somewhat faked through use of additional '/' seperators, though if I understand correctly, they're not semantically significant.
