You're confusing two different things. Pointer off screen != wiimote can't see the sensor bar.
The field of view of the IR exceeds the dimensions of your TV. That's how the little arrow moves around the edges. But don't feel bad. Most of these people have no clue of what they're talking about.
Wiimote sends very little information to the console, but that small amout of info can be used in pretty smart ways. Different games might have their own ways of interpreting the data from wiimote to make the game more playable. And same goes for the opposite: Many games don't use the data that well, which leads to bad gameplay. Wii and wiimote get the blame for bad coding.