The orientationsensor automatically adjusts between portrait and landscape mode in most applications when the device is tilted, and the 2-Axis Accelerometer is great for controlling games that need simultaneous steering and acceleration.
Now, you can lock the orientationsensor and pretty much never encounter this issue again (we can't ever really imagine needing to read a text-based book with adjustable font sizes in landscape mode, after all), but it seemed worth mentioning given it goes unchanged since the previous version.