Actually, many owner's manuals have named dishwashing liquid specifically as a recomended product to clean your car. I don't know if it is still a current practice or not, but my '99 Integra manual said it as well as my '97 Mustang. I'll have to look at my Corolla manual to see what it says. I think we know better than to take auto manufacterers advice when it comes to car care products, but it isn't a wonder why so many people have used dishwashing soap to wash their cars for so long.
Interesting.
I just checked some owner's manuals for our vehicles.
Products to use:
1998 Chevrolet Blazer - liquid hand, dish or car washing soap. (Mild detergent)
1999 Honda CR-V - Mild detergent such as dishwashing liquid or car wash soap.
2000 Honda CR-V - Same as for the 1999.
2000 Pontiac - Use a car washing soap.
2004 Pontiac - Use a car washing soap.
Like Jngr said, information to lead one to think dishwashing liquid is OK.
I can't remember the manufacturer, but I'm sure I have read where one says to use plain water. They don't recommend using anything but just the water.
Back on topic.

I don't/wouldn't use a sealant over a wax.
I personally don't use a wax over a sealant.
FWIW, the WOWA sealants do claim to work over a wax.