Microsoft is just following the lead of its competitors, though, and that four years plus of support seems downright generous in comparison with Apple, which ceased support for the original iPad just two years after its launch. The 2010 tablet was never updated to iOS 6.
If Microsoft offers annual hardware iterations for the Surface, then customers will likely be itching to buy a new one by 2017 anyway.
During the Surface RT and Surface Pro's mainstream support phases, Microsoft will offer hardware repairs (free under warranty), replacement parts and units, and telephone-based support for the Windows 8 tablets.
Windows 8 itself will be supported for the full 10 years (five mainstream, five extended) of support, according to a support website FAQ.
It states that "the software embedded in [the Surface device] is subject to the Microsoft software lifecycle support policy, as is any software that is installed or downloaded on that Surface device."