That's pretty much the conventional wisdom on the subject.I take a bit of a different view about the Surface line. I think that it was developed for two reasons - one was for Microsoft to hedge against a future where their x86 tablets weren't competitive. By building the Surface on ARM they would not be caught completely unprepared for one potential path to the future.
The real key of the issue, however, is slightly different. At the time of the original Surface's release, Intel was far, far behind ARM in power consumption and not showing any significant motivation to change. Their ATOM chips were the only thing available in real low power, and they were being let to rot on the vine. The development of Windows for ARM was Microsoft's way of forcing Intel to get on board with low-power chips. It worked, and now low power, high performance x86 tablets are a work-able reality. Hence there is no longer any good reason for Microsoft to produce ARM devices.
Maybe Intel is close enough, maybe not. I would not be taking that iron out of the fire yet and mobile phones is not the presence needed. The next challenge is the important one.
Well there's OS's and then there's OS versions... Already we have the Windows 10 Surface Hub version, and the phone version, and the tablet version, plus the Home, Pro, Enterprise versions, the Embedded & IoT versions, etc. but they are all going to be called Windows 10. Don't kid yourself, these aren't the same any more than 250 distributions of Linux are the same.Well it looks like with Windows 10 they are moving in the direction many said they should have gone from the start - one mobile OS for phones and basic tablets, and regular Windows for more powerful tablets. The original question with the Surface RT was not just 'why?' It was 'why a third Windows OS?'.