Actually, it's not, physical addiction takes place when certain chemicals (µ opioid agonists, such as alcohol, barbiturates, nicotine, etc.) bind to µ opioid receptors. And the chemicals that can be released when playing poker due to excitements are most likely catecholamines (adrenaline, noradrenaline and dopamine) which can only cause psychological dependence. So forget that myth once and for all.
Neither alcohol, barbiturates, or nicotine have any activity at µ receptors, so you are mistaken. Most drugs, like gambling, exert their addictive effects through secondary activation of the mesolimbic pathway and endogenous dopamine release.
This is exactly correct! Physical and Psychological addiction are the same thing. They take advantage of the reward centers in your brain, which makes you want to have more. Gambling can easily do this (and it does), video games can become addictive this way, and even those crappy mobile games use the same tactic. All they do is trigger the reward center and cause your brain to release some dopamine, and your hooked, trying to get your next hit. That is facebooks business model actually.