It is not cut and dry, x amt of pages. Read the document and when you do some research it is hard to predict ... remember this is for a commercial duty expensive printer. There simply are too many variables.. Just remember the saying, the candle that burns the brightest burns the shortest. So if your intent is to blaze continuous printing of the highest resolution with 100% color coverage as in high quality photographs on a non stop basis, be prepared for a shorter life. How much shorter? Hard to tell, even Canon can't put a finger on it exactly either.
Don't know why Canon published the guideline of print head life.
Whatever the reason it may be but if you believe in the numbers Canon said in the guidance I have an advice for you. Just keep printing and get as much printing as you can out of the print heads and make sure they die before the guidance says they will. Then ask Canon to replace them free of charge. It shouldn't take a genius to tinker the simple logic behind this. No? Hummm... Can anyone tell me why my cousin's BJ3000 is still rocking and rolling after 7 years of doing so? Now that we are in this thread again let's do a rational discussion or debate on it.