This has nothing to do with wiring; we are, essentially, all wired the same way (ignoring, of course, the outliers: e.g. people with an improperly developed nervous system [CIPA - Congenital Insensitivity to Pain with Anhidrosis]). There are, however, various reasons you might have different effects on different people:
Muscle Mass – While this is not a direct inhibitor of reception of pain by any means, the muscles do serve to protect the weaker points on the body (as does the general format of the body itself). Large muscles make it difficult to strike between them into the indentations of the body, or the points at which nerve clusters are exposed. For example, the biceps and triceps serve to buffer somewhat the ability to strike into the nerve clusters on the arm. This is generally the weakest form of resistance, as this sort of definition also accents the location of nerve centers (the indentations between muscles).
Hormone Levels – Hormones are the electro-chemical signals of the nervous system. Various factors, such as environment, genetics, diet, etc. can all contribute to increased or decreased hormone levels, some of which are responsible for the neurotransmission of pain. An adrenaline response is a great example of this; elevated hormone levels producing a form of anesthesia.
Drug Use – A far more common than realized reason is drug use. Many drugs work by inhibiting or altering the neuro-chemical signals. I don't imply simply PCP and other illicit drugs here, but prescription medications (For example, Lyrica) as well.
Neuron Damage – Nerve clusters, like the rest of the body, can be damaged. Repeated injury can "wear out" a nerve, preventing the feeling of pain from that location as a means of self-preservation. Burn victims often suffer intense pain often because of the memory of the pain, their nerves long since destroyed, before drowning with pneumonia. Many people who were particularly clumsy as children (thus falling a great deal) seem to share a distinct resistance at the knees and elbows that may suggest nerve damage occurring in childhood from repeated trauma.
Conditioning – Through mental conditioning, we can become more resistant to pain. Whether we call it conditioning, self-hypnosis, or anything else, it boils down to asserting ones will upon their existence. In whatever ways one may do this, they are essentially thinking (consciously or subconsciously) themselves out of pain.
Pressure points are not some mystical, magical tool; they are a difficult concept of inflicting massive amounts of pain when possible. You should not strive to strike or grab or tear at a vital point, but rather train so that all your strikes find these points automatically.
A Note About Use of Pressure Points
"You should be able to hit your opponent's kyusho [vital points] at any time." – Hatsumi Masaaki
"Create your own kyusho" – Hatsumi Masaaki
In Appendix 1 of Valery Momot's Anatomy of Life and Death: Vital Point of Human Body (sic), a series of prints taken from Fujita Seiko's book on Kyushojutsu are reproduced showing the vital points given in various Chinese, Japanese, and Okinawan arts. The placement of the points is varied, sometimes over a relative [scaled] foot in difference between the two points labeled as the same kyusho.
I will admit here and now: I do not believe in Qi meridians. When I was creating my kyusho charts for my training manual, I sat down with that book, my own diagrams, and Gray's Anatomy of the Human Body and found the nerve clusters that corresponded to the points. I stepped through diagrams that I barely understood to find the ways I could recognize the body's weaknesses. I visited the Bodies exhibit in Vegas to sketch and learn anatomy.
It's an error to think that people are different. It's our search for identity that makes us believe we are unique and special. Underneath the skin, we still exhibit the same characteristics, excluding the outliers.
Kyusho are one tool. We can strike, grab, press, pull, and otherwise manipulate these points, and not all manipulations produce the same results. Ultimately though they are simply dense clusters of nervous tissue that are easily exploited; however, our bodies are full of this sort of tissue. Do not rely on solely these points, but instead explore the ways in which the rest of the body can cause horrific pain just as easily.