Agreed - line spacing is a function of the font metrics; it is not fixed for any given point size, for example. You can see this quite readily by duplicating a paragraph in different fonts at the same point size. Not only do character widths vary but so too do their line heights. You can demonstrate this by creating a paragraph with some text that spans around 1.5 lines, duplicating the paragraph and applying different fonts to each of them, then running the following macro to retrieve the line heights:
Code:
Sub Demo()
Dim oPara As Paragraph, sFirstLn As Single, sLastLn As Single
For Each oPara In ActiveDocument.Paragraphs
With oPara.Range.Characters
sFirstLn = .First.Information(wdVerticalPositionRelativeToPage)
sLastLn = .Last.Information(wdVerticalPositionRelativeToPage)
MsgBox sLastLn - sFirstLn
End With
Next
End Sub