Wax is a "sealant" by definition (provides a weather-proof layer of stuff on the paint) but the sealants you refer to are all synthetic, usually acrylic polymer-based, and generally tougher than waxes. They literally provide a hard, thin layer of totally clear "plastic" over the paint, much like painting wood with acrylic (water-based) paint creates a synthetic barrier. Downside is that they're synthetic and tend to look synthetic. Like wrapping your car in Saran Wrap is one oft-heard comment.
Waxes are natural products harnessed in solvents in a bottle of gunk and provides a warmer, less plasticky shine on paint. Downside is they generally don't last as long before rubbing or wearing off.