We just spoke with Microsoft, who once again confirmed that the HTC HD2 will be left out of the Windows Phone 7 Series upgrade path, as will most–if not all–current generation devices. The reason being the hard-standed requirements on the 3 buttons–Start, back, and search. While many HTC HD2 users will be upset by the fact that they will not be able to move their devices forward to the next-generation OS, I understand–and appreciate–Microsoft’s decision on this as it does create and enhance the user experience to have a consistent 3-button arrangement.
Users who purchase any mobile device should not buy under the assumption that they will get an upgrade to the next generation OS. While Google, Microsoft, and Apple have been generous with providing upgrade paths, that’s not the norm. New software–whether it be from the OS or via third party applications–may require stronger, modern hardware and some software requires specific hardware sets that may serve to define the user experience.
In the MIX10 press question & answer set, we also discovered that Microsoft may be standardizing on sensors, which may be another reason for a lack of upgrade path–the company may be requiring some uniformity in sensor hardwares to create sensor APIs for developers to access in Windows Phone 7 Series.
Source