I can understand why they do this. the IP4200, like others in the range, has a separate print head. On the cheaper models the print head is incorporated within the more expensive cartridges. Using compatibles here will do no harm, but they may damage the head on the 4000 range. Canon are simply covering themselves. I have an IP4000, and I will use Canon cartridges until the warranty expires in the not to distant future, when I will change to cheaper compatibles, which I have already purchased.