Really Microsoft had very little prospects of getting it out the door before Christmas in time to get it into the hand of the hardware people which could get it into the hands of the cell phone carriers.
Someone at I think AT&T as they are feeling the iPhone exclusivity hammer coming... suggested that since they couldn't get Window Phone 7 to run inside the 8GB constraints on the on board memory... they use the SD card in RAW format and switch its mode to the other mode SD cards have... its a one time switch.
On the other hand, Linux and OSX have been able to do that for a long time. Windows just recently (with Windows 7) just got the native ability to do that. Its cheap and easy.
Why do you think you are starting to see Windows Workstations with 2 Primary disk drives for the OS... one with traditional storage another used for "special purposes" also being an SSD used in RAW mode.
Windows can address *FAR* more virtual memory than real memory. Why not! So... they just did it with Windows Phone 7.