I think this is about maturity & experience. When I played for my school chess team, going all the way to mate was important for me & if my opponent resigned, I felt cheated. But that was forty years ago & now I feel exactly the same if I win by resignation or checkmate.
In one of my earliest games on this site, an opponent fought on doggedly until the end, even though his position was utterly lost. I remember thinking at the time that it was very honourable of him but I also wondered why he'd bothered.
When you know the game's up, don't waste your opponent's time & resign-that's what I always do & anyway isn't it more dignified?
Of course if you're playing a child then that's another matter.....
Actually I don't agree to resign a game after losing just a piece or the queen. However, calling someone "sore loser" just because he resigns the game doesn't seem right to me.
Maybe this game can be an example for a "sore loser";
http://www.youtube.com/watch?v=aMiLXbGxUgs
End of the game Mato says: "Bardeleben didn't resign. He stared at 25-Rxh7+, shot a glance at Steinitz, and without a word got up from his chair and left the room. He didn't come back.... Stainitz had to wait for Bardeleben's time to run out.."
In blitz games resigning is very rare and I would never resign because getting a draw can maaay be possible under some preassure. However, tournament games are way different because most of the time, the clocks will be having at least 2 second delays that means if the position lost it is lost. You cannot gain time playing faster than your opponent. You can only stall the game.
It is not clear how the Steinitz - Van Bardeleden ended. It is clear that Van Bardeleden was upset with the actions of the spectaters at Hastings and filed a formal protest. According to some accounts, he gave Steintitz a note indicating that he was protesting the spectators and not Steinitz.
http://www.chesshistory.com/winter/extra/steinitzvonbardeleben.html