The addressing of the Display memory to the character positions on the display can vary depending on the rows/columns organization and manufacturer of the display. Most 20x2 displays will work as you describe with the commands being 0x80 and 0xC0 corresponding to the starts of Row 1 and Row 2. For the 20x4 display the row start commands will most likely be 0x80, 0x94, 0xC0 and 0xD4.
I have seen displays that use the 0x80 for Row 0, 0x94 for Row 1, 0xC0 for Row 2 etc.

However it depends to some extent how the manufacturer connects the LCD glass to the 44708 chip. The best scheme is to have a display in hand and run some tests by sending 80 characters to the display memory in a counting sequence and observe what gets dislayed where.
Hope this helps.
Michael Karas