The difference here is that Vietnam veterans were not given any honors and were, so the stories go, treated very badly by some of the people they met. Even when they were not personally treated badly, they were certainly not honored because the nation did not know how to deal with the idea that the US had failed to win a war.
By contrast, in wars since then, people have been very careful not to repeat this mistake. Even those who oppose the war have been careful to treat those who fought with respect and honor. We have seen, for example, many professional and college sports teams doing special things to honor veterans who have returned. On sports broadcasts, especially around the holidays, the TV networks will show film of soldiers out in Iraq or Afghanistan watching the games. There are messages of support for the soldiers that are broadcast during those games.
In all of these ways, soldiers in the Iraq War (both those who return and those who are still over there) are treated with much more respect and honor than the Vietnam veterans were.