Yes - I noticed the same yesterday, but didn't get a chance to post. There were 4 total non returnees for reasons other than graduation. 2 Dmen (Larry Playfair's son 'Dennis Playfair' and Goldberg) who both received minimal playing time so I assume that is the reason for their departure.
The 2 you mentioned were much bigger losses. Manley was a senior and definitely would have been a starter. He tended to be paired with our big guns as a distributor, energy, garbage goal guy - can't say he was really a 'highly skilled' player despite his stats looking pretty big. We'd all get a lot of assists if we were passing to Zach Vit. That said, he will still be missed for the reasons we both mentioned and it is too bad his career appears to be over. The bigger lost IMO is Lubczuk as he would have maybe been our #2 defenseman. For those who don't remember, he was on the all rookie team along with his fellow freshman blueliner Nate Brown. Three of the six members of that team were Ice Knights (David Ripple being the other). We lost 3 starting defenseman so Brown, Caradonna, and Lubczuk were certainly expected to step up big time this year. Also a bigger loss because I was looking forward to 3 more years of him on the team vs. just 1 for Manley. Of course, maybe it is a "get academics in order and he'll be back" situation but I don't have any information.
Not all is lost of course as certainly a lot of other skilled players and recruiting class looks quite solid, but definitely would be better to have had them on the team.