That is a stupid thing to say, and you are a stupid person for saying it. We're talking about a peripheral that improves the accuracy of a measurement the Wiimote already takes, attitude!
It sounds like you don't know what the Wii MotionPlus is and how it works. The accessory adds a multi-axis gyroscope to the Wiimote. It's by combining data from the sensor bar, the accelerometer and the gyroscope that accuracy is improved. It doesn't magically make the existing data more accurate.
In the previous generation, almost every game supports at least 480p, and in the case of the original Xbox, the system comes with a fantastic scaler for those people who don't already have one in their TV.
Wrong. A minority of PlayStation 2 games supported progressive scan. The situation was much better on the Gamecube, but lots of games still lacked support. Only on the Xbox was progressive scan support a standard that most games supported. Unfortunately, in Europe progressive scan support was almost non-existent as the option was stripped out of 99% of PlayStation 2 and Gamecube games, while the option doesn't even exist on a PAL Xbox.
You say "at least", but only a small fraction of Xbox games had support for 720p, and even fewer for 1080i. Once more the option doesn't exist on a PAL Xbox.
There's this thing called automatic gain control, I hear we've had it for some decades now, and it would be nice if Nintendo discovered it.
Maybe there's a reason it wasn't used? It's not an instant solution, and I can imagine it making the remote consume more power.