Funny, isn't it, that Katniss is the one who gets all caught up with mockingjay and songbird symbolism when Peeta is the one with the golden voice? Throughout the book, Katniss admires Peeta's ability to make speeches:
[…] and then I think of it, what Peeta can do much better than the rest of us. He can use words. He obliterated the rest of the field at both interviews. And maybe it's because of that underlying goodness that he can move a crowd – no, a country – to his side with the turn of a simple sentence.
I remember thinking that was the gift the leader of our revolution should have. (23.76-77)
Peeta speaks as naturally as Katniss hunts, but his skill isn't called for in the arena like hers is. It's the luck of the draw that she ends up as the face of the revolution, all the while thinking that Peeta would be much better suited for the task.
Peeta is a bit of a contradiction: he's one of the kindest and least selfish characters in the book, but he's also one of the best liars. When the tributes have their final televised interviews before the Quarter Quell, Peeta steals the show by producing not just one but two excellent lies. These lies, which explain that he and Katniss are already married in their hearts and that she's pregnant, are so effective that the audience seems likely to explode. Katniss' reaction shows she's not even that surprised:
There. He's done it again. Dropped a bomb that wipes out the efforts of every tribute who came before him. Well, maybe not. Maybe this year he has only lit the fuse on a bomb that the victors themselves have been building. Hoping someone would be able to detonate it. Perhaps thinking it would be me in my bridal gown. Not knowing how much I rely on Cinna's talents, whereas Peeta needs nothing more than his wits. (18.28)
Here Katniss contrasts herself negatively with Peeta, envying him for being able to "drop a bomb" all by himself rather than needing the help of someone else's "talents" like Katniss thinks she does. Katniss remembers that Peeta used this time in the interviews to his advantage during the previous Games, too. In both instances, he recognized that his special skill was manipulating language, and the best place to deploy that is outside of the arena, not in it. Were it not for his alliance with Katniss, he'd be easy pickings in the arena.
Although he's a great liar and public speaker, Peeta uses his gifts for selfless causes. He thinks of the people he and Katniss have watched die with sorrow and wants to honor their memories. Just think about his speech in Rue 's district during the Victory Tour:
"It can no way replace your losses, but as a token of our thanks we'd like for each of the tributes' families from District Eleven to receive one month of our winnings every year for the duration of our lives." (4.75)
He also does the crazy/stupid/foolish/brave thing of painting a picture of Rue in front of the Gamemakers, saying that he "'just wanted to hold them accountable, if only for a moment [...] for killing that little girl'" (17.18). Peeta doesn't think about the consequences of his action. He wants to do the right thing, which is to point out how wrong Rue's death was, and who really caused it: the Capitol and the Gamemakers.
Peeta also wants to save Katniss' life as much as she wants to save his. He voluntarily enters the arena to take care of Katniss, and he does everything he can to convince her to place herself over him. One of his tricks is to give her a picture of her family and Gale, telling her that she needs to think of how much they need her. Not only that, Peeta seems to signal that it's even OK with him if Katniss marries Gale:
Peeta's intention is clear. That Gale really is my family, or will be one day, if I live. That I'll marry him. So Peeta's giving me his life and Gale at the same time. (24.80-81)
Is anybody really that selfless? It seems like if anybody could be, it's Peeta, and by taking this kind of action he is proving just how much he loves Katniss.