I think Memorial Day is the only holiday that has something of a ticking clock included with it. Independence Day also has temporal significance insofar as it there can be important anniversaries of the date, but that's mostly based large, round numbers. The bicentennial was a big deal. The years afterwards, 201, 202? Not so much.
With Memorial Day, the passage of time is more sublime. I'm old enough to remember when World War I veterans were honored guests at the parades and ceremonies. The World War II veterans were well into middle age, but still active. The veterans of Korea and Vietnam were somewhat ambivalent, and the latter group was struggling to define both their identity and relationship to military service as a whole.
Slowly, inexorably, the demographics changed. The Great War generation faded away, making its last stand in nursing homes or with single representatives. The "Greatest Generation" started to slow down, and behind them the "conflict" veterans became more organized and strongly represented.
Today, the Vietnam and Korean War veterans are the old guys, and the World War II survivors are so scarce as to render their reunions pointless. My Gulf War/War on Terror generation is now moving into the familiar position of recent service, but this time it has a strange twist because our wars took so long. In my case, "serving for the duration" took 20 years.
Our losses were also comparatively light, which was probably why the wars were able to drag on as long as they did and end so ignobly.
All of which leads to feelings not unlike those of the Vietnam generation. I joked with one of my uncles (who was in Vietnam during the Tet Offensive) that he'd manage to lose only one war; my generation lost two of them