In Catching Fire, we see that the tributes from District 1 are Cashmere and Gloss, who are siblings who won the Hunger Games in successive years.
But why did they do that? They surely must have known that it would end in the death of at least one of them. Given that that are Careers, they might survive to the end and face the choice of having to kill one of themselves.
Plus, it isn't like District 1 has a shortage of victors. Others who would want the glory might have volunteered too. It would be okay if only one had to go.
So why did they go to their own deaths?
It may be said that since the Capitol allowed two victors the last time, they might do so this time too, but that seems too risky, knowing the Capitol almost went back on it's word the last time.
Is there any confirmation that the rule modification was extended to the next year as well? It isn't like the Capitol really wanted to let Peeta and Katniss live, Katniss just forced their hand.