We often have found with many of the new routers and Windows 7 and later will default to IPv6 for all their Internet lookups when browsing the web. The issue is that seen by many is that the resolution of names in the URL are delayed until an IPv4 is used to complete the lookup. This problem started after an update by Microsoft that caused IPv6 to be preferred over IPv4.
Microsoft released a Knowledge Base article on this issue, KB2533454 - Resolving Internet connectivity issues after World IPv6 Launch (June 6, 2012). This KB article contains a Microsoft FixIt tool to change the preferred IP version from IPv6 back to IPv4