If you'd use 1,3-dimethoxybenzene in the manganese catalyzed acetonylation there will be several products.
Like 2,4-DMP2P, 3,5-DMP2P and 2,6-DMP2P. These may serve as precursors for, let's say 2,4-DMA, 3,5-DMA and 2,6-DMA, but not for the DOB/DOI derivatives.
Using 1,4-dimethoxybenzene only yields 2,5-DMP2P, which of course is a very valuable precursor for the DOB/DOI derivatives.