Casey may be pro-life, but is he more of an economically minded person? Santorum has spent a lot of energy on socially conservative causes, and while Casey might share some his views on those things, it doesn't mean he would fight as hard for them, or become the social conservative leader in the Senate, as Santorum is.
Does it matter?
His father was largely ecoonimical, but he was chastized by the Left.
Could he appease the voters by simply ignoring social issues then and focusing on economic ones?