Ellalan got the title Manu Needhi Cholan because he has executed his own son to provide justice to a Cow. Legend has it that the king hung a giant bell in front of his courtroom for anyone needing justice to ring. One day, he came out on hearing the ringing of the bell by a Cow. On enquiry he found that the Calf of that Cow was killed under the wheels of his chariot. In order to provide justice to the cow, he killed his own son Veedhividangan under the chariot as a punishment to himself i.e. make himself suffer as much as the cow. Impressed by the justice of the king, Lord Shiva blessed him and brought back the calf and his son alive.
http://en.wikipedia.org/wiki/Elara_%28m ... dhi_Cholan
Now Manu Needhi is nothing but Manu dharma shastra or Manu neeti in Tamil.In Telugu grammar which is derived from Sanskrit to a certain extent,'t' is parusha or tough sound whereas 'd' is sarala or easy sound.Somehow there seem to exist many easy sounds in Tamil.
Manu neeti or Manava dharma sastra or Human righteous laws/morals were said to coded differently in different areas as large empires never existed for hundreds of years throughout the sub-continent.The above stories of Ganesh and Ellalan proves the same even though Hindu law givers quote that what they express is the will of the Swayambhu or the Self-existent.Now both Vishnu and Shiva are said to be self-existent.Which self-existent one gave the law,noone knows.And how come there are so many discrepancies in laws of different areas is anyone's guess.