Alzheimer's Drug problems

According to Ed Silverman in his Pharmalot blog, Myriad Genetics is discontinuing development of Flurizan, their Alzheimer's drug. But there is a bigger issue at stake here than just the failure of one drug. As Ed writes in his blog:

The failure is significant because Flurizan was one of the first drugs to reach late-stage testing that tried to prevent the buildup of amyloid plaque in the brain, a focus of much research into Alzheimer’s. Whether this will raise questions about other drugs targeting amyloid plaque remains to be seen.

Wyeth and Elan are jointly developing a drug that tries to block amyloid plaque and, so far, have generated considerable interest, even though preliminary Phase II results were mixed. Lilly is also in late-stage testing of a drug that works simlarly to Flurizan

Bottom line....are all these companies chasing after the wrong cure for Alzheimer's?