The source of this code is obtained by typing its name at the R prompt.  The output is

    function (x, thresh = 0) 
    {
        pks <- which(diff(sign(diff(x, na.pad = FALSE)), na.pad = FALSE) < 0) + 2
        if (!missing(thresh)) {
            pks[x[pks - 1] - x[pks] > thresh]
        }
        else pks
    }

The test `x[pks - 1] - x[pks] > thresh` compares each peak value to the value *immediately succeeding it* in the series (not to the next trough in the series).  It uses a (crude) estimate of the size of the *slope* of the function immediately after the peak and selects only those peaks where that slope exceeds `thresh` in size.  In your case, only the first three peaks are sufficiently sharp to pass the test.  You will detect all the peaks by using the default:

    > findPeaks(cc)
    [1]  3 22 41 59 78 96