dhenry:
wouldnt at least one LED manufacturer jump on the bandwagon and say " you don't need a resistor with our LEDs " and sell more ? Perhaps they know something, being manufacturers.
They do, that's why you never hear an LEd manufacturer (reputable ones) who says "you have to use a resistor with LEDs".
Because both statements ("you have to use a resistor" and "you cannot use resistors") are wrong. Whether you should use a resistor or not is application specific and needs to be evaluated specifically.
Just common sense.
Wrong.
Manufacturers supply things called "datasheets" with their parts. In the datasheet there's always a section titled "Absolute Maximum Rating". The values in there are determined by people who know stuff about their product and know what power is likely to damage it.