Really?

From Zotero's site:

  Data syncing is free and unlimited, and it can be used without file syncing.

Looking at my own Zotero account, I can confirm that all metadata storage is free and not counted (I am using none of my 300Mb storage in my account according to zotero.org, despite syncing metadata for several thousand bibliography items). The only storage Zotero seems to count is attachment storage, and that's all synced via my WebDAV.

What am I missing here?