I think the punk is more absent in steampunk, but the steam is often a bit absent too.
I guess I don't terribly like steampunk at the stage where it's a bunch of people trotting around in top hats and pith hats with pointless cogs glued on, which is what it often seems to be. I can enjoy it as a celebration of engineering and creative inventiveness, or as an interesting subversion/punk way of looking at that period and its culture... but I feel like too often in the UK at least the steampunk community is a bit of an "I just want to pretend I'm an upper class Victorian" thing and doesn't do either. Which is sort of fine, but it doesn't appeal to me much and I think can feel more exclusionary to people who originated in countries that the said Victorian elites were... not entirely pleasant too, to put it mildly.
I agree though that dreadpunk doesn't seem to differ enough from steampunk to be a worthwhile label.