New players would have no idea why certain blocks have mass and others don't.
At least, speaking as new player, outdated tutorial, totally abstract crap-fantaisic name of ressources, messy craft GUI, and passive/boring crafting process are more real issues imho than object's different mass.
Actually, in real life, I don't know why one glass of liquid lead is heavier than one same glass of water but I don't care. I just assimilate that as fact.
So if in SM an armour is heavier than an ice cube, I wouldn't wonder why, I'll just learn and integrate that as fact aswell.
And, personally, I don't like simple game who babysit players like if they were all newborn babies. If they really want play a game, they will experiments, tries and learn how play it and eventually understand game mechanics.