You mean the entire Mass is sung, or just that there is more singing such as the Hallelujia, Our Father, hymns, etc? Either way, I suspect it has to do with each individual parish and the presence or lack thereof of a "liturgical committe" (don't get me started, heh).
When I went to Easter Sunday service, they pretty much sang things you wouldn't have thought they would do. I also come from the "Old School" where when you said "The Lords Prayer", you didn't have your arms stretched out and head up, but kept them folded in front of you, head down in a remorseful manner.