It isn't even that Alito and Roberts are noticeably more liberal that Scalia, but that they're noticeably more professional. Scalia was a transparent partisan who made decisions based on the effect they would have for his acquaintances or his pet ideas; Constitutional literalism was his rationale, not his driving motivation. Only Thomas is so bankrupt a judge currently on the court, and he doesn't have Scalia's intelligence, knowledge, or wit—traits he used pretty much for evil.