When Brian said he was curious about my sandbox rendering "Blessed are the pitiful, because they will receive pity." I realized, hey, I'm still curious about that one too. Liddell & Scott's Lexicon glosses 'elehmwn' as pitiful, merciful. Related forms are glossed slightly more often with the idea of pity than mercy; the central idea (whatever it actually was) seems to include compassion, feeling pity, and the sense of giving charitable alms. A larger study is not within my reach at the moment, unfortunately, but here are some thoughts.
First, I'd definitely imagine pity was more common in the ancient world than mercy. The connotation of mercy seems to imply power, in that mercy is something we can choose to give or withhold. Kings and judges deal in mercy, but any beggar can pity a fellow beggar. At least, so it goes in practice. But no matter how seldom alms were given, beggars asked for them daily, constantly. A common hope could have as much influence on word usage as a common experience, so these thoughts might be a wash.
The Oxford English Dictionary references both Pitiful and Pitiable going as far back as about 1450, and the double meaning of pitiful goes back exactly that far as well. Technically, pitiable is still in usage today as but I think we can agree the sense of "pitiful" as "merciful" has pretty much faded away. Liddell & Scott worked from lexicons going back to 1797 but the L&S itself has been revised as recently as 1996. Assuming nobody slipped up at Oxford, there's probably a reason L&S continues to list pitiful and merciful as separate glosses.
Since the OED emphasizes the double meaning of pitiful and the L&S offers a complex meaning for 'elehmwn', I think we should probably expect that Matthew intended us to read Jesus' Beatitude with a double meaning as well. Blessed are the merciful. Blessed are the pitiful.
You need mercy. You receive mercy. You learn, God hopes, to show mercy.
There's a natural progression in that sequence that is not always universal, but it is common. Sometimes in life, a person is challenged to show mercy and then they find God. I definitely think Jesus meant to challenge his disciples and the crowd on that mountain to show mercy, but I absolutely know they could already relate to needing mercy, because their lives were indeed somewhat, if not extremely, pitiful.