Does anyone know why Mashable's twitter post links use the address "http://on.mash.to/?" http://on.mash.to/?" What is the purpose of using link shortening if y

Does anyone know why Mashable's twitter post links use the address "http://on.mash.to/?" http://on.mash.to/?" What is the purpose of using link shortening if you add superfluous characters that don't make sense "on"? What does "on mash to" mean?