Re: This is probably...
Lots of companies have legacy apps that will never get ported to ARM.
Microsoft is hoping everyone will buy Windows phones and tablets, which may use ARM chips.
This allows your company Windows phone to still run your legacy x86 app on an ARM chip.
Probably no one is going to buy Windows ARM phones or tablets for their whole company, but this is Microsoft trying to make it slightly more attractive.
Also, if ARM based servers suddenly become popular this could be useful, but that's not looking very likely.