Series resistors in smps after Bridge rectifier
You are correct that if the R1 resistor has adequate voltage and power rating then R2 is not needed.

This appears to be an application suggestion in the data sheet for the IC. The IC designer is assuming the the designer of the SMPS that uses it will want to make it for the lowest possible price. In this case, two cheap resistors are usually somewhat cheaper than one adequate resistor.

The low cost 'ordinary' or 'cooking' grade resistors usually have a max voltage of 200v, totally adequate for low voltage circuits, but too low for this use.