The technology just isn't there yet.
The problem is that's an input box, and I would guess they didn't have masked/filtered input boxes in the ui framework that changes display as you type in them. It's not hard, but it's not trivial either and don't they have better things they could spend 8 hours on
My solution would be to put the input textboxes on the bottom of the ui (that STILL do not show decimals) but have each split window show the display value with decimals for each side and update as you type in the gold amount...
While we're on the subject of ui and numbers... wht they hell does the new bulk bod system need to display 6 decimal precision for the points???