Genetic Imprinting and Cell differentiation
What if imprinted regions are immune to being wiped? Also, you may be confusing DNA methylation, and histone methylation (?). Classical biochemistry posits that DNA methylation states can be transmitted from a dividing mother cell to both daughter cells because after DNA replication the two daughter chromosomes will each be hemi-methylated, and a DNA methylase that finds a hemi-methylated site will methylate the other strand (like a corrective editing mechanism).
The third thing to consider in your question is that parental imprinting is established in the germ line. In terms of wiping other epigenetic marks during early embryogenesis, the only ones present would be the ones involved in gametogenesis.  In other words, as far as we know, genes activated in muscle development are never expressed after fertilization in the zygotic cells that will give rise to the primordial germ cells, so those muscle-specific epigenetic marks don't need to be wiped off in the embryo. Neither the sperm nor the egg ever expressed muscle myosin, etc.