Not to mention, he even says himself that it was " ... the similarities are a bit more than striking. That's not a huge issue until you release everything together - the icons, the colors, the UI elements, whatever."
DMCA notices are to enforce against copyright infringement only, not as a tool for organizations to abuse in order to remove content which they think is "too similar", if this was the case, businesses would simply send their competition DMCA notices for being "too similar."
He also stated that because DesignModo "removed some icons" which LayerVault thought were the most blatantly infringing somehow implies guilt, as opposed to just someone trying to handle a dispute in a friendly manner.
I'm not a designer, and I haven't heard of LayerVault until now, however unless some very damning evidence is presented, I feel like every statement he's making is essentially digging a deeper grave.
EDIT: Having looked at the examples of the claimed infringement which are now surfacing, this is even further evidence that this is misuse of the DMCA. At most, this would be a civil / trademark dispute.