Fan-out of the Intel 8086
I actually wire wrapped an 8088 (which is similar) shown below and I did have to pay attention to fanout (my max fanout is 5, which you may be able to tell on some of the processor pins)

Two words, noise margin, the current supports 20 chips: true but the noise margin does not. I really wish they would say something about capacitance at this point but they didn't, which also plays into fanout (if you have to much capacitance it increase your rise and fall time although this is not as much of a problem for standard logic families because they reduce capacitance) 

If you read the rest of the chapter:  


Source: The Intel Microprocessors by Barry B Brey