The SharePoint 2013 March Public Update requires additional configuration steps to complete a SharePoint App Store deployment.
In this article, “Enable apps in AAM or host-header environments for SharePoint 2013”, http://technet.microsoft.com/en-us/library/dn144963.aspx The additonal steps are indicated.
New-SPWebApplicationAppDomain
$contentService = [Microsoft.SharePoint.Administration.SPWebService]::ContentService
$contentService.SupportMultipleAppDomains = $true
$contentService.Update()
Iisreset
Solving SharePoint Issues - Eric Schrader 