Clarke figured to be a likely choice because he played on the last five teams and has won twice on the European Tour in the last four months.
Instead, Faldo went with a pair of Englishmen at the end of the Johnnie Walker Championship.
"I've been watching these guys through the summer," Faldo said. "Ian is a very determined guy. I love his attitude and what he did at The Open — that back nine he played with the intention to win and had that emotional feeling."
Poulter was the runner-up at Royal Birkdale, one of only two top-10s he has had all year. He skipped the Johnnie Walker, where third place or better would have earned him a spot on the team, and instead played the Deutsche Bank Championship on the PGA Tour and missed the cut for the second straight week.
"Maybe I should have gone to play Gleneagles, but I stuck by my word," Poulter said. "Looking back at the time I made the right decision for me, but it was so difficult to choose the right thing to do and it's obviously been a very difficult decision to try to get across."
Faldo said he had been keeping an eye on Casey and waiting for his putting to improve.
"I've been watching Paul play and he has been playing absolutely the best through the summer," Faldo said. "He has an extremely good record in the Ryder Cup and, going back, the Walker Cup."
Oliver Wilson clinched the 10th and final automatic spot by finishing in a tie for 10th place at Gleneagles, while Justin Rose and Soren Hansen also qualified to make their debuts at the competition.
Padraig Harrington, Sergio Garcia, Lee Westwood, Henrik Stenson, Robert Karlsson, Miguel Angel Jimenez and Graeme McDowell had already made the team.
Nick Dougherty would have had a chance to make the team by winning the Johnnie Walker Championship, but his 69 left him in seventh place.
Clarke has a 10-7-3 record in five Ryder Cups, and he was the emotional leader in 2006 at The K Club in Ireland when he won all three of his matches just a month after his wife died of cancer.
He did not win again until the BMW Asian Open at the end of April, then routed the field at the KLM Open in Holland two weeks ago.
Clarke said he respected Faldo's decision and said he would be supporting the European team.
"Obviously, I am disappointed that I wasn't selected, but I have dealt with much worse and it will make me all the more determined to make the team that will play in Wales next time," Clarke said in a statement. "There was a qualifying period, and I didn't make it automatically, so you will not hear any sour grapes from me.
"I couldn't have tried any harder and I devoted myself to the European Tour to give myself the best possible chance," he added. "But although I have won twice this year, it obviously wasn't enough."
British Open and PGA champion Padraig Harrington was cleaning out his locker at the Deutsche Bank Championship when he was asked for comment, and said initially he could not think of anything to say so soon after the announcement.
"Two great players who will strengthen the team," he finally said of Casey and Poulter.
U.S. captain Paul Azinger said he was surprised by Faldo's picks.
"I thought it was between Casey and Poulter. I thought Clarke was a lock," Azinger said. "But the guys he picked are really good. His dilemma is a nice one to have. You look at all the guys he had to choose ... I don't have that. It's not like I have a bunch of veterans with monster records at the Ryder Cup."