Which of the structures mentioned in that article is not found in humans? They all exist in humans, albeit not as large or as developed as in Giraffes. The one-way blood vessel valves, for example, exist in humans for the save reason they exist in giraffes. We also have spinal processeses, and other ungulates have them as well-developed as in giraffes.
Likewise the fascia on lower legs exist on other animals, including man. As giraffes grew, everything got bigger, tougher, etc. It would be useful for giraffes to have more neck vertebrae, but that did not happen; that would require greater changes than making things bigger and more robust.
If we look at various existing and extinct members of the giraffid group, we see that neck length gets relatively greater as the body gets absolutely bigger. This is called "allometry." So pronghorn antelopes are not very large, and have necks only slightly longer than other ungulates. Okapis are large animals and have relatively longer necks. We see that in fossil giraffes as well. Bigger speciments have relatively longer necks. There's no magic to making it work, though. It's just making various parts bigger and more robust.