It's not completely out of date. We do, after all, have limited RAM, HD and CPU to execute our programs. I could probably implement something that is very inefficient very easily. We want to pay attention to the speed, but we don't want to dwell on it (to the point of micro-optimization) or consider it the final word in language merit.
I could write a script that slurps things into a linear array and do a painful linear search every time I want to see if an element exists. Or I could use a hash to do the same thing in much less time...