This could just be an annoying issue of how a word is used. Words pick up multiple meanings over time. Certainly "budget" can be used in the sense you say, but

This could just be an annoying issue of how a word is used. Words pick up multiple meanings over time. Certainly "budget" can be used in the sense you say, but "The Budget" is a term for a political event, in the UK and probably Canada which includes other things - much as those of us who like cleanly defined terms would prefer it otherwise...