It's really strange that you assume that all derailleurs are the same and that one set of instructions will work for everything... If I only owned one bike, I wouldn't have a problem. Unfortunately, four of the five bikes I own have derailleurs and they're not all the same.

Just looking at front derailleurs, there are a number of factors to take into account: SRAM versus Shimano, high-clamp versus low-clamp, and top-pull versus bottom-pull. IIRC, I've got three bottom-pull derailleurs (two high-clamp, one low-clamp) and one top-pull derailleur. I guarantee that your instructions don't work for all of the derailleurs I own... I just can't remember which ones are which!

The score is much the same with rear derailleurs: Shimano versus SRAM, high-normal versus low-normal, etc. Again, I'm not sure your advice applies to to all the different permutations. All of my rear-derailleurs are low-normal, but I want to say that SRAM and Shimano put the limit screws in different locations due to the differences in the shifting mechanism. Or maybe it's a difference between MTB and road bike? Again, I can't remember which is which.

In addition, for SRAM road components at least, the order of adjustment seems to be important. My experience was that if I followed the instructions exactly, adjustment was super-easy. Fiddle with the limit screws in random order and it was very difficult to get things dialed in precisely. Shimano seemed much more amenable to random twiddling.