A good portion of drunkenness is purely psychological. Tell people that fruit juice is alcoholic, and they start acting drunk, even though they're sober. I imagine it's mostly that, plus the different alcohol concentrations.
For some people that's definitely true, placebo is a real thing after all. But it's not like that with everyone, and even if "booze is booze is booze" is true, just like with cannabis, there is more stuff in the drinks than just alcohol, that might also change the effect you get from drinking.
