2 reasons for the resistor:
- it is easier to produce a stripe coding printer than a text printer.
- It doesn't matter how the resistor is soldered, the rings are always visible. (also from a distance)
Thinking about this , many of us older guys can't read the codes from a distance on the smaller resistors ( or sometimes up close without a magnifying glass 
)
And if I want a leaflet/business card printed, its cheapest with one colour, and goes up for more colours.
If manufacturers used white on a darker background ( as they do on smd caps and res ) you would think it would be cheaper.
They have pad printers that can print on curved surfaces, and have been printing a band plus text on diodes for 50 years now.
I am guessing the diodes are rolled over the ink transfer medium ????