Hmmm... Doesn't Excel recalculate when you finish editing a cell? And isn't the cell containing $500 highlighted for editing (& might it not have contained $0 prior to editing)? Poor art direction, but nothing wrong with the operation of the spreadsheet. But don't let that spoil your fun!
There sure are a lot of people with absolutely no sense of humor or irony jumping to Microsoft's defense on this one. So you signed up just to make public that you don't get it at all?