I will tell you too, Alain, that we interaction designers often feel a sense of being in the minority. We struggled for some time just to be allowed to call what we do design, so we may sometimes use the word in a chauvinistic sense. That is certainly what Cooper chose to do in Inmates, but for him it was a rhetorical strategy to put interaction design on the map.
I hang around with and work closely with many interaction design people so I understand their pain. There are many developpers out there (few agilists I would hope) who even today, believe that usability is just a matter of slapping a GUI over a backend.
But the solution to this impass is certainly not to turn things around and advocate that we should be designing the GUI and then just slap a backend underneath it. Yet this is exactly what Cooper proposes in "Inmates". Advocating such a process can only piss-off those "unenlightened" developpers and get them even more set in their ways. The solution, as you and I obviously agree, is for interaction designers and developpers to engage in continuous day-to-day cooperative problem solving.
BTW: This is exactly what has happened with Agile and testing. QA people used to feel like their message didn't get across to developpers. There were all kinds of misconceptions on both sides of the fence. QA people felt that programmers didn't care about quality, whereas programmers felt that QA people didn't understand the pressures of code writing and meeting deadlines. But Agile methods (XP in particular) solved the issue by bringing testers into the trenches and having them collaborate on a day to day basis with developpers. As a result, developpers in an XP team tend to be much more sympathetic to quality issues, and in fact, they litterally live by unit testing. And yes, there is still room in XP teams for testing specialists, who can advise developpers on how to write good test and who do independent testing.
I'm glad to see that many interaction designers are taking a similar approach and I trust that it will completely change the way developpers think about and react to issues of usability.