[BitMastro]

The height is calculated automatically for the rows that are visible and you can fix it to a certain amount.

So, as screigh said, you won't have the wormy effect on contact list, artists, songs, etc. because each row is always x pixels. The same happens if you have for example a series of thin and thick rows because they average out.

Another reason why using a set of constants is not common is that we have different screen sizes and different resolutions to deal with, so what looks like a good value for a resolution might not be the best for another.