Actually, there is visually no difference between the Epson 1440 setting and 2880. There is under magnification, but not to the naked eye. On a scanner though, this allows you to print larger images and still maintain quality output.
eg. a 1" by 1" image scanned at 300 dpi will look the same as one scanned at 1200 dpi. But, the 1200 dpi image will allow you to blow it up to a much larger print before you start losing quality. Granted there wasn't much to begin with. On the other hand, if you scan an 8x10 at 1200 you end up with an immense file. If you print it at 8x10 you won't see a difference in say 300 dpi than one scanned at 1200. I hope that was clear.
Right. There's a big diference between the psudo-continuous tone technology of thermal or tricolored laser systems (not color laser printers but light jet systems) and the ink jet systems.
I think the root of this question is the ambiguity of the term DPI. Someone wrote a book about halftoning. They suggested thinking of scanners as dealing in Samples per inch. I think printers should be grouped with Halftones, dealing with spots per inch. Apples per inch VS. Oranges per inch.