It is. And it's one of my complaints, if you read the original article. They came up with this ABI too late in the game (most software has been soundly tested, or even entirely developed, on amd64), and with too little common points to either x86 or amd64 to make it easy to port.
So the (IMHO little) benefit on the data cache utilisation is made useless by the huge effort and compatibility issues brought in by having a full new ABI. Which is probably why the original presentation "sold" x32 as a closed-system ABI, not a generic one, like it seems people expect it to be right now.