I think the posts have captured some of the essence of these two.
Newbury can score some at the AHL level. He's tough - not a great fighter but will fight. As Holland said, he's a good AHLer who could spot fill the 4th line for short spells - though the Griffins may well have others better to call up.
Williams is a more interesting case. If he got top six ice time in the NHL, I think he'd handily pop 25 goals. He has a heck of a shot - probably the best shot in the Leafs organization. And he has a nose for positioning himself to get it away or will fire it on an off foot to surprise a goalie. There is zero doubt in my mind that he has NHL goal scoring talent. If the Wings suffer an injury to a top 6 finisher, they have a guy they can call up and the offence won't skip a beat. He's not a 3/4 liner - either he's on a scoring line or he's in the minors.
Burke wanted to make the Leafs tougher. Williams isn't a big, tough player and therefore, wasn't going to fit the mould for Burke's team.
When he showed up for the AHL, they knocked his skating speed. He worked on it and I don't think it's an issue. His skating seems fine to me.
The more recent knock that concerned the Leafs brass was his two way play and winning puck battles - in coach Wilson's system. With the Wings style of puck control, that may not be as big of an issue. I'm interested to see what develops. When he was up last season, there were not a lot of goals scored against when he was on the ice. I think he's improved but because the team already had too many soft players, he got sent down.
Williams may end up toiling in the AHL for his career so I make no promises. But I still think he has some sort of a slimmer chance to crack the NHL because of his scoring ability. In that way, at 25, he's still a bit of a prospect who just might surprise a few folks. Regardless, he can be a fun player to watch.