Via Stefan Goßner, Microsoft is now supporting stretched farms in SharePoint 2013. Perhaps customer feedback has forced them to reconsider.
Update on Stretch Farm Support in SharePoint 2013
Per http://technet.microsoft.com/en-us/library/cc262485(v=office.15).aspx#hwLocServers, support for stretch farm topologies SharePoint 2013 was unsupported. As a result of our continuous efforts to review and update our product performance and capacity boundaries, we are pleased to announce supportability for a limited set of stretch farm topologies under the definition of distributed topologies. All of these topologies are based on a prerequisite of minimal (< 1ms) latency between components of the farm (see also http://technet.microsoft.com/en-us/library/cc748824(v=office.14).aspx#Section4 (SharePoint 2013 articles to be updated accordingly)).
Topologies that do not meet this definition remain unsupported and are not under consideration for review at this time.
From Plan for availability (SharePoint Server 2013):
Redundancy and failover between closely located data centers configured as a single farm ("stretched" farm)
Some enterprises have data centers that are located close to one another with high-bandwidth connections so that they can be configured as a single farm. This is called a"stretched" farm. For a stretched farm to work, there must be less than 1 millisecond latency between SQL Server and the front-end Web servers in one direction, and at least 1 gigabit per second bandwidth.
In this scenario, you can provide fault tolerance by following the standard guidance for making databases and service applications redundant.
The following illustration shows a stretched farm.
Stretched farm
