I noticed that most, if not all, of the albums I used the volume analysis on indeed have a negative replay gain. As you pointed out.
But it is a different story for individual tracks. I have seen a lot of positive values between them. And it is right there where the clipping will occur when the album gain is not used when playing back music.
For now I will just recalculate the album gain for all albums with negative values. Personally, I only use album gain, since most of my music are DJ mixes.