Speed, youth, experience. You really expect Emmerton to score 50 pts with Holmstrom and Abdelkader for 8 minutes a night? Cory is fast. He will improve this year.
Experience compared to which players he would be competing against? Mursak is young and faster if those are Emmerton's best assets. I don't expect Emmerton to put up big numbers playing on the 4th line, but that further elaborates my point really. His offensive ceiling isn't high enough to assume a bigger role and ideally you would like your 4th line to do something other than nothing, which is what the Red Wings got last season. Putting Abdelkader at center, adding Tootoo to the mix, plus having Eaves/Miller as well gives you a useful 4th line that actually provides energy while also having the ability to contribute offensively. Emmerton is solely a skill player, with minimal skill.
A surprise would be if Emmerton somehow even makes the team.