Lets look at the facts we have today.
1. Nokia deal with partnering with Microsoft and today Nokia looking to sell HQ facility for cash influx.
2. Build conference was a last minute decision around June/July timeframe when windows 8 phone idea starting becoming real.
3. Microsoft already demoed tablet with windows 8 at last years conference. Tablet is not enough to make a headline this year. (even ARM based one)
4. The PC / laptop / ultrabook is not dead nor is there a future where mainstream business/engineers/accountants use tablets to do work. More investment still will go into PC's.
5. Xbox is dominating now and Microsoft is not going to let this platform get old. Tight lips here on this one but you know the new Xbox is coming very soon.
Based on this I think Microsofts phone will be a temporary item for prototyping and not for general audience. Surface tablet also will be phased out once vendors get on board to understand what Microsoft wants them to deliver. Microsoft will stay Microsoft and not become MicroHard. Making hardware is not where they want to go. But they want the hardware vendors to know that if they promote Google Android for much longer that Microsoft will play hardball with them.