Me too, I agree that 1/4" is 1/4" and a scant 1/4" is a scant 1/4" the world over.
I think that what's happening is that some patterns can be sewn with any seam allowance, as long as it's consistent. (Log cabin is an example. Likewise 9-patch, 4-patch, etc.) The resulting blocks will only be exactly the right size if the seams are a scant 1/4", but it's okay if they're all a little smaller or a little larger, as long as they're consistently the same. For this reason, some people will tell you that you need to finish a project on the machine on which you start it. If you learn to sew a consistent scant 1/4" seam, you can sew on any machine. You will have to measure and adjust for each machine until you get it right, but the result is worth the effort.