I don't think Joe Dumars is ready to sacrifice Tay + Rip solely for cap space. I believe he feels his team is at the opening stages of their development, and that if his acquisitions develop the way he hopes, that he'll be able to put another contender out there.
I think he's delusional and should drop Tay/Rip's contracts right away ... but I don't think he has any interest in that possibility at this point in time. Maybe by the end of season, at the earliest, he'll come around.
As for the trade -- Great trade for Detroit. Great trade for Sacramento. Bad trade for Houston. Solid trade for Boston. I think I'd prefer it without Nocioni.