While, I have no idea why it was removed, the Microsoft Research Lab has restored the Microsoft Touch Mouse Sensor API.
Touch Mouse Sensor API - The Microsoft Touch Mouse supports multitouch gestures via an integrated sensor. The Touch Mouse Sensor API SDK is a small library intended to enable students and researchers to experiment directly with Touch Mouse sensor output.
Using this SDK, you can create your own applications consuming the 13×15 sensor image. The SDK includes C# and C++ samples demonstrating how to read and manipulate sensor data.
NOTES: To use this SDK, you need Windows 7, Visual Studio 2008 or Visual Studio 2010, and a Microsoft Touch Mouse. This SDK is provided for research and educational purposes only and is not intended for commercial use.