The OEMs didn't care about customer experience, they just wanted a "Vista!" sticker they could slap on as many machines as possible. MS had to know these machines would make Vista look bad; they should have resisted the demand. But they didn't, so tons of people bought machines they thought would run Vista acceptably, only to find out they did not. So they (understandably) thought Vista was just a dog that couldn't run well even on "Vista certified" hardware.
But Microsoft gave them the gun by agreeing to the OEMs' demand to create a "Vista Capable" classification, for machines that were too underpowered to run Vista well (see http://www.crn.com/slide-shows/channel-programs/206905984/tr...).
The OEMs didn't care about customer experience, they just wanted a "Vista!" sticker they could slap on as many machines as possible. MS had to know these machines would make Vista look bad; they should have resisted the demand. But they didn't, so tons of people bought machines they thought would run Vista acceptably, only to find out they did not. So they (understandably) thought Vista was just a dog that couldn't run well even on "Vista certified" hardware.