Cahill is now with the Australia squad for the Asian Cup.
The inspirational Australia midfielder has hit nine goals this season, three times as many as forwards Ayegbeni Yakubu, Louis Saha and Jermaine Beckford combined.
Moyes said: "It's a great return for a deep-lying forward or attacking midfielder.
"He's really been the only one that has contributed with a serious goal tally.
"We've had people like Bainesy [Leighton Baines] getting a couple of goals which is not bad but, in truth, we have not had any of the other main people stepping up to the mark.
"We have got to get some of other players in the team to."