The trick with a 53-man roster prediction is that you have to consider core special teamers and gameday inactives. You have 46 gameday actives and a certain number of them have to fill your kick return/coverage teams. These guys also fill the bottom of you depth chart, but they get on the field for ST. This means that if you are keeping Slater, White, Cole or the like, they aren't going to be healthy scratches.
The rules require 7 players to leave their uniforms in their locker on gameday. These guys are either injured or happy enough (for now) drawing an NFL paycheck that getting a Sunday off isn't an issue. That would include most of the rookies and a few vets (MacDonald, Deaderick). Not so much for guys like Larsen, Gallery, Scott and Carpenter.
This is why guys like Dennard, Tarpinian, Forston and Bolden may end up sneaking on the roster. High upsides, won't be a locker room disruption if they aren't active, can play in an emergency. Happens every year...and every year people are shocked by it.