“For Surface devices, any Surface software installed, embedded or downloaded on the device is subject to the software lifecycle support policy for that software (unlike other HW devices such as Xbox) … The hardware support lifecycle policy applies only to the Surface hardware (and as stated above not the Surface software). For Surface devices, that policy affects only the tablet device and hardware based accessories (and for example not to soft goods accessories such as cases).”
To give this some perspective, Apple’s original iPad which was released 2 years ago is no longer supported from iOS 6 onwards, which means that four years for the Surface RT tablet certainly sounds like a device worth keeping and using, assuming it does not break down in the middle.