Comment 16 for bug 630639

In case 1 it looks like Adobe Reader detects that it is a very thin line and draws the line with a cosmetic pen. Cosmetic pens don't support caps and joins but if the line is 1 device unit wide this won't matter.

In case 2 and 3 it looks like when a geometric pen is used the stroke is converted to a path, flattened, then filled.

It should be possible to change the cairo win32 printing surface to perform a similar optimization as Adobe Reader. ie use a cosmetic pen if the line is 1 device unit wide and the user space transform is a uniform scale. Inkscape can use gtk_print_context_get_dpi_x/y to determine the printer device units.