Why are some apps on the market incompatible with my device?
The Android Market has various filters which are applied to the apk in order to find out if the App will run on your device. The most obviously one is the Android version you are on (also called the SDK level).

But this is not the only criteria. There are others like:


Screen Size
Software libraries

Google API
OpenGL

Particular hardware features that are required

Bluetooth
(front) camera
Vibration



Unfortunately it is not that easy to find out why an App "isn't compatible" with a particular device, even for the developer. There are some tools that an developer can use to find the current filter criteria for an .apk but this will not tell him why the Android market doesn't show an app on a device explicitly.

In your case, the small screen size seems to be the reason. You should e-mail the developer and ask him to fix this, if it isn't intended.