18 months support for Windows RT devices?

At the introduction of Windows Phone 8, there was an statement that all of the new Windows Phones 8 devices will get at least for 18 months of software support. Because of that Windows RT runs on an ARM processor just like a Windows Phone and because they are based on the same Windows 8 kernel, I think that Windows RT devices are restricted to limited time of software support.

What do you think? Will the Windows RT devices get 'Windows 9' or other future updates?

(sorry for my English, it's not my mother language)