Yes, that's right.
There is something in the formula of calculating the Zig-Zag - respectively Fibonacci, that prevents the indicator to give too meny signals. It is works like smoothing the indicator. If you notice, neither Zig Zag nor Fibonacci are in the list of MetaTrader's main indicators.
I'm not shure, here is place to discuss the source code.

See the next pictures:

We see here, the selected bar 7/11/06 07:00 is Fibo top (line 0% - see the green line form the nex bar)

but here:

The signal was moved to: 7/11/06 14:00