The difference between this and Halo is Play Anywhere. It's certainly doubtful that it would have pushed digital share to half, but it's reasonable to assume that digital share would be better than the current 30% average month 1 assumption for non Play-Anywhere titles.
You know I was halfjoking but I don't really think the difference is that big with any other high profile game. I'd say play anywhere seems to be a really marginal thing that gets the echo chamber effect on gaming sites.