Cathy,
The reason the 55188 from Agri-Fab cannot be shipped to California is because the engine does not meet the environmental standards set forth by the CARB act.
Agri-Fab would be the one responsible for all warranty questions and I have no clue why they would offer less of a warranty with Home Depot. Hopefully you are seeing a typo. I would either call Home Depot or ask Agri-Fab by calling (800) 448-9282.