When a pattern calls for a scant 1/4" or a 1/4" they mean whatever size seam you need to achieve the result you mention in your post. What some don't understand is it's a moving target. You can mark your machine, or use a specific foot, but if you change the thickness of your thread or fabric, you may have to adjust your markings. You give a great example on how to check, here's another one:
http://www.quiltingboard.com/tutorials-f10/achieving-accurate-1-4%22-seam-allowance-t89997.html
btw, you are not beating a dead horse! each time this question is posted, I'm sure a light bulb goes on for somebody out there!