It was the Japanese at work. They realize that not only would it be cheaper to weld the joints in instead of making them replaceable, but that they would also make a **** ton more money when the ball joints wore out, and people were buying new a-arms for $100 or more vs just buying a ball joint for a fraction of the price.
I don't know if the 87's actually fit on the other years, the frames on the 87 and 88's are different. All the aftermarket a-arm companies claim that their arms only work on 89-up.