There are things in the XDI dictionary that are not in this schema and vice versa. That's not necessarily a problem or even an issue. However, there might be merit to aligning them as closely as possible.
For example, the Spectra Table (why is it called Spectra Table rather than Spectrum Table?) has an entry called temperature while the XDI dictionary suggests nomenclature for 15 other extrinsic sample parameters in the Sample. namespace.