In the playground between my ears, I had a random thought that no amount of basic research has been able to satisfy this burning question that pesters me like a mosquito.
A Duke’s wife is called a Duchess.
Baron’s wife a Baroness
A Marquis is a Marquess (sp?)
But why is an Earl’s wife called a Countess? Why not an Earless?
Because earless sounds funny?
Well, that’d be a good answer except that the wife of a Sultan is a Sultana.
picmr
Shirley, sometimes you make me giggle like no other. Thanks! A very good question for which in all my wisdom 
I have no answer for.
The British title of Earl is the equivilent of the European Count. The word “count” comes from the latin “comes”, a Roman Imperial Official. There were counts in Britian at 1 time. The “Count of the Saxon Shore” that frequently appears in Arthurian stories was a historical title. But unlike on the mainland the term did not long survive the Roman period.
I am unsure of why the word was not brought back after the Conquest. Perhaps the elegant differentiation between earl and churl was appreciated. Later attempts to bestow this title were not popular with the noble bestowee. It sounded foriegn. It should be noted that these whiners were likely to be great nobles and as such not as eager as those who later took the proffered title of viscount.
As to the reasons for the English countesses, the females tend to be more in tune with “Continental” fashion 
I am the count! Von, two, three! Ha ha ha ha!
Because the title Earless is spelled earless, meaning without ears.
The wife of a Marquis (or Marquess in English spelling, I think, please correct me,) is actually a Marchioness.
Barons and Earls were native noble ranks in England; Dukes, Marquesses, and Viscounts were all imported later. I suspect the Earls were not likely to change their native title to some foreign term. Why they didn’t also use Count, I don’t know (since they did later add the ranks of Duke and Marquess, both of which come above Earls [lucky them.])
Why Countess? Everyone else’s answer seems to make sense. The term did get some widespread use for an English “heir” during the reign of King Stephen - when he was fighting cousin Matilda (or Maud) for the throne. She called herself the Empress because of her first husband, her enemies called her “Countess of Anjou” because of her second husband. Make of that what you will.
Besides, you can get much better dirty jokes from “Countess” than from “Earless.”
Thank you all for taking my mental drival seriously. I hate it when one of these questions pester me and I don’t have the time or wherewithall to do proper research.