I agree. It isn't just the machines...it can be the difference between the 1/4 feet that you use.
In fact, I stopped using a 1/4 foot because it never gave me a true scant 1/4 seam. I now use a vintage sewing machine that will move the needle both to the right and the left and the first thing I do before sewing is to use my little metal ruler to line the needle up up on the scant 1/4 inch line. (It only takes a couple of minutes.)
Another problem with getting a good scant 1/4 seam could be the thread. If (because of using different machines) you use different threads, one thread could be just a bit thicker than another thread. Some of my projects get put on hold where I pull the thread off of the machine to do some repair work with a different thread. After awhile, I forget what thread I was using on my quilting project. When I put thread back on the machine, I run a sample seam on some scraps to check out my 1/4 seam just to make sure I'm doing the same width as I did in my earlier blocks.