:P
Well... they are the same for the Developer/Publisher.
Piracy
Some dude buys a game, the Developer/Publisher gets money from that sale. This dude then makes a copy of the game, uploads the game to the internet and hundreds/thousands/millions of other dudes get the game by downloading it from the internet.
Result:
The Developer/Publisher doesn't get anything from those hundreds/thousands/millions who downloaded the game.
Buying used
Someone buys a game, the Developer/Publisher gets money from that sale. This person gets tired of the game, goes to Gamestop or whatever and trades his game in. Someone else buys that used copy of the game, gets tired of the game and trades it in again... repeat this process unknown times :P.
Result:
The Developer/Publisher doesn't get anything from those who bought the game used.
Renting games
Well, you know... someone goes to a store, rents a game, plays the game, returns it to the store.
Result:
The Developer/Publisher doesn't get anything from those who rented the game.
Overall:
Someone gets a game but the Developer/Publisher doesn't get anything from that someone :P
Now... if you're going to buy used or rent a game... why don't you just pirate the game? :P I mean... the Developer and Publisher won't get anything unless you buy new. The only difference is that you'll have to spend money if you buy used or rent a game and you'll also make Gamestop or whatever store very happy with your money :P You'll also get a legit copy of the game if you buy it used... too bad the Developer and Publisher didn't get anything from that "sale"... if you pirated it it would've been the same for them.
Remember, this is "Buying used/Renting games = Piracy" in the sense that the Developer and Publisher won't get money in any of those situations.
What do you think?
P.S: Sorry if I can't stop using ":P", lol.