Because otherwise man and chimp would have 100% the same genes. And no, if you knew a little bit of biology you would not say that the gene where one part was different is counted in the above. All genes for similar functions in different species have differences between them. That is why the blood of different animals cannot be used for transfusions in each other. No the 200 genes (or 300 or 700 if the higher numbers said by some to be in the human genome) are totally different. That higher species have new genes should not surprise us. The simplest known bacteria has some 500 genes. Therefore a lot of new genes had to have been created from the time of the first life to now. Let me remind you again how long it would take to just make one gene in man using the most favorable assumptions towards evolution a 1 with 42 zeros behind it years.
It is the actual coding of genes for similar proteins, and more traditionally the proteins themselves, that are mostly compared across species. You can't just count the genes. Of course, you can also learn a lot comparing the location and content of viral DNA introns. That's another line of evidence that humans and chimps are recently diverged.
Your model is a waste of arithmetic. You multiplied or divided by everything but your birth date but I've learned not to look at the fancy footwork.