Why has A-Uno rev3 two different 16MHz resonators?

I have a Duemilanove with one 16 MHz crystal. It has a FTDIO as USB serial.

Then I have a Uno rev3 with a CSTCE16M0V53-R0 resonator attached to the a328 and a atmega16u2 as USB serial with a much larger 16 MHz crystal in metal housing attached to it.

  1. Why are the resonators different? Why not use the same type for both controllers?

  2. I have never tried but is it not possible to let both microcontrollers use the one and same resonator?

Could the board be production optimized or is there a reason for this different choise of components?

/best regards

The USB serial interface chip(*) needs an accurate clock I believe to handle USB, it has a crystal,
forget what frequency.

The ATmega processor itself probably has a ceramic resonator still (to save money), rather
than quartz crystal - though boards do differ. The Duemilanova had a different USB serial
chip which derived its timing from USB I believe, so only the ATmega had a crystal and it
was quartz, much more accurate.

(*) The interface chip happens to be another AVR microcontroller as it happens.