"the impetus is on abc to do xyz"

I see the word impetus used frequently this way. Here is a headline:

http://fcw.com/articles/2001/08/28/omb-impetus-is-on-agencies-to-fund-egov-efforts.aspx

"OMB: Impetus is on agencies to fund e-gov effort"

I don't see a definition of impetus which would support this. Should another word like onus be used instead?