There's obvious analogues. Cram seems to be meth, more or less. Novacoke is obviously Coke+. I personally reject the idea that deepweed is marijuana, though... okay, yes, it's called
weed but the effects of the obviously awakened deepweed are quite different from the effect of good ol' fashioned weed. I do find it highly amusing that it's one of the few drugs outright forbidden as opposed to restricted, though. I guess even by 2075 they haven't managed to legalize it.
Personally, I assume the modern-day drugs are still there, and either a) legalized and/or easy to find and cheap or b) so flimsy in comparison to their new-and-improved versions that they don't warrant space in the rule book. So you can have a pot-smoking Shadowrunner, you just don't suffer negative dicepool modifiers or get to pick up an addiciton quality or anything. It's just a character quirk.
On an out-of-character level, I assume it's just bad PR to have "rules" about cocaine, heroin or methamphetine addiction in an RPG rule book. Like others said, putting "nova" in front of "coke" helps defray some of the vehement anti-RPG craziness. Granted it's on the downslope these days, but I imagine this was a factor in previous editions.
