If you purchase 'AutoCAD LT 2013', you get a license to use our software. If you purchase 'AutoCAD LT 2013 + Subscription', you get a license and a service, which is the Autodesk Subscription Program. As you may have noticed, the cost is different.
The Autodesk Subscripton Program includes many benefits, among which the upgrade to the next version and direct technical support. To know more about these benefits, please visit this page.