I'll write about the TPS. The TPS is basically a potentiometer. The 5V reference is used so there is a constant fixed voltage for the sensor. That way, when the TPS is at 1/4 travel the output voltage is exactly 1.25V, when the TPS is at 1/2 travel the output is exactly 2.5V and when the TPS is at 3/4 travel the output is exactly 3.75V. Well, theoretically anyways.

It's be much harder to use these sensors if the reference voltage wasn't a fixed voltage. Say you tried to just use the battery voltage. Well, that can vary 1-2V and also contains all the switching noise and alternator ripple and other stuff such as that which means you have to constantly try to filter and correct for those variations. So, regulate it down to 5V and filter it so you have a nice steady voltage for the sensor and then you can just read the sensor output and know what it means without worrying about the reference voltage fluctuating. Same reason a dedicated negative wire is run from the sensor back to the ECM. It eliminates system noise and chassis ground connection issues. You'll see that the early systems used the exhaust system for the negative of the O2 sensor and then later systems used a dedicated wire and that change would have been for the same reason.