Um, no.
You can use an 85 watt Mafsafe adapter with an Air, just as you can use a 45 watt Magsafe with a 17" MBP. In the former, the Air simply draws the power needed and much of the capacity of the 85 watt Magsafe is unused. In the latter, the MBP's battery won't charge quickly (if at all), and any shortfall in required power will be made up by the battery. But in neither case will the Magsafe damage the battery or the computer.
The wattage specified on a Magsafe adapter is the maximum it is rated to constantly deliver--it DOES NOT automatically supply that wattage all the time. Rather, the Macbook's power management circuitry and software determine how much power is required and draws that from the battery and/or Magsafe.
You are correct that you generally cannot mix and match supply voltages (from the wall, so to speak) without either a transformer or specialized equipment that is built to adapt to different voltages. Which, interestingly, the Magsafe adapters are--if you look on your Magsafe it will say "Input: 100-240V - 1.5A 50-60 Hz. Thus, it can handle an input voltage of between 100 and 240 volts, will show a maximum current draw of 1.5 amps, and can use either 50 Hz or 60 Hz alternating current (AC).