Not sure what to say other then I know someone that is trying to use Maya with a very high degree of accuracy and it seems he is finding the same issue.
As a test I just created a platonic tetrahedron and tried to create it with a side length of 1.0 by setting the length in the creation options and it came out .99997 even in the creation node. I snapped a distance measuring tool to any two verts and got the same measurement .99997. You can change the precision in the channel box settings from the default 3 but although it does display more digits it still seems to be pretty casual about the actual accuracy. I then went into the creation node and changed it to 1.0 and although it display 1.0 in the creation node it was still measuring .9997 when I used the distance tool.
I am trying to find out more as I have often wondered if there was some limitation to Maya's accuracy and I will let you know what I discover.
all info is welcome....I am glad you have found a workaround. I will forward anything I hear back from the autodesk forums.