Part of it is that some of the other countries have cash in both documents. And not every country has a Treasury Board, which actually requires a rather detailed expenditure plan before you can actually go through the estimates.
You have to understand the control that Parliament is exercising over the spending. In our case, Treasury Board is the authority for expenditure approvals, and before you get into the estimates you have to make that step. In other countries, the nature of the estimates document is not the same.