In september 2012, it was found that people using Safari on iOS devices and performing search on Google appeared to publishers as if they directly landed on the website and not via Google. The problem that has previaled for the past 10 months has now been resolved as Apple has upgraded iOS to support "meta referrer" tag.
The up gradation however doesn't solve the "not provided" issue, wherein Google could strip the search term to find the site that passed from referrer to the publisher. But, the upgrade will at least make people appear that they came from Google search and not as direct visitors.
Referrer data is not provided in iOS 6 and is hidden when one clicks from Google search results page to a website. However, the referrer data is provided in iOS 7. Whether you have signed in or out, searching directly on Google.com or via the omni search box present in the mobile Safari, referrer data will always be passed virtually on iOS 7.Safari is Again Providing Google Referral Data in iOS!,