The oils in the polishes need to be removed prior to applying Paint Sealant. This is not needed for waxes and glazes, since they do not bond to the paint like synthetic sealants do.
A synthetic sealant like Paint Sealant gets its long protection life by actually bonding to the paint. In order to get the best bond, the paint needs to be cleaned of all oils or other contaminates.
I prefer strip washing after polishing and prior to applying sealant, since it does a better job at removing the oils. Depending on technique and how many clean towels are used, it is possible that a wipe down with Isopropyl Alcohol will not remove all the oils. For example, just using one towel for the wipe down will likely just be spreading the oils around, rather than actually removing them from the surface.