The "unique" title for the most uncommon weapons has been the staple for the Diablo franchise. These weapons were marked with gold writing and carried with it a unique icon. Uniques in Diablo 2 varied in usefulness, though the most desired uniques such as The Grandfather, Windforce, The Oculus, and Stones of Jordan maintained desirable stats and quickly became staples for their respective classes (before the age of runewords, of course).
With the coming of Diablo 3, a few changes have been covered over the past years of development that regards the idea behind unique weapons and armor. The first of which is the change of the title "unique" to "legendary" and the color from gold to orange. These changes present a linear similarity to the success of World of Warcraft and its item's color scheming. Obviously, this parallel has woken the beast within the Diablo 3 community upon its initial announcement. After months of debate, the beast was lain to rest - but with today's comments on the Battle.net forums, the beast has been re-awakened.
Bashiok takes the beast on again by explaining their philosophy behind this "monumental" change, as many believe that the gold lettering was a wonderful personification of grandieur within a desirable weapon.
Unique items in Diablo II were only "unique" in that only one of them would drop per-game. Using the term "unique" to describe them implies many things, none of which are likely to be true.
World of Warcraft uses the word a bit more intelligently in that it is indeed unique in that your character can only ever have one of them.
World of Warcraft uses unique and unique equipped for character balance, so that the designers know what items a character can have equipped at any one time. Balance is important to us, but probably not to the same degree that we would want to restrict use of dual-wielding two of some awesome legendary sword. For instance.
[p]If I would be so bold to say, the change "from Unique to Legendary" personifies the progression of Blizzard as they traverse the ground between Diablo 2 to Diablo 3. While I lament the loss of the gold text for the rarest items, I accept the validity and logic in Bashiok's statements. And of course, he always tends to leave such statements with the enigmatic "but nothing is set in stone" refrain, so there is always time for change.
ANd don't forget, there is much to look forward to, much to be revealed, and a whole cartful of information awaiting us this year at Blizzcon.