Help interpreting a histogram in Gimp

[linux_matt]

There is a certain type of histogram which shows a very flat graph with few pixels for any tone (light, mid or dark). This type of histogram (shown below) relates to photos with pale/washed-out colours. I have often wondered why this histogram appears to indicate that the photo actually has less pixels than another photo with the same resolution. Shouldn't the histogram show the same number of pixels for any image? I think I am interpreting the information incorrectly and would be grateful for advice on this