I'll add one thing to Jon's post specifically about the Vertex for anyone interested since they are no longer producing the Ecrin-Roc. I have both the slightly older version and the newer version at work. Both are a suspension helmet. Both have a slight cutout around the ear area to allow for hearing protection and the slots for these above the ear. The older version has a single knob adjustment in the rear, whereas the newer one has the dual knobs on the side of the helmet. I personally prefer this particular type of adjustment. The newer vertex also incorporates some foam in the lid, maybe a four inch square directly above the top of your noggin. If you look inside the older vertex or at the ecrin-roc, you'll see a grid pattern in the apex of the helmet. In the newer vertex this is where the foam is placed. Whether or knot that grid system still underlays the foam, I don't know. Also the newer vertex has the slot for Petzl's new blade mound headlamps and also a slot in the rear, which is I assume for a power source a-la the Duo. A slight difference also, that cavers probably don't care about is that while the addition of a face shield is possible for both, on the older vertex it attached to the ear protection. On the newer vertex I believe it attaches seperately so that if you don't want ear protection, but you want a rated face shield (think ice climbing) you can do this. The newer vertex also comes in more colors I think
All in all the newer vertex is the Ecrin-Roc, with a few more bells and whistles. It ISN'T any lighter.
Another tradeoff for lightweight foam lids is that they aren't near as tough as far as daily use goes. I bought my wife a Petzl Meteor (lightest helmet at the time, maybe still is) and on our way to or from a climbing trip we checked it in a bag and it got what looks like a compression crack just above the ear, like a lot of weight thrown on it. Now granted, it was packed in a bag stuffed with cams and other hard, pokey climbing gear, but it isn't something I would have worried about with a different helmet. The plus side of foam lids is that if they are damaged, you can SEE it. There's no guessing.
Though I LOVE how light the meteor is, since I have the tendancy to sort of abuse my lids (sit on them, kick them around, throw them in a truck with some chainsaws, entrust them to baggage handlers), I'll stick with one that's a little burlier.