The decision to disallow a '1' for the last dimension was made during the April 10, 2008 phone conference.

From the summary of the phone conference:

Dimensionality:
This attribute will no longer include trailing dimensions of 1.
In other terms, if we have an Nx1 data array we should use:
dimensionality = 1;  dim0 =N
rather than:
dimensionality = 2;  dim0 = N;  dim1 = 1