It goes back well beyond thirty years. My grandfather told me a story about driving from NC to LA when I was about 6 months old and using a Coka-Cola to get the bug guts off his windshield. That was 67 years ago then. Having bug guts and how much does seem to depend on where you live. Here in the steamy, humid South they are more prevalent than up North where I previously lived.
It is generally true though another factor for less squashed insects may be better aerodynamics on modern cars, so more of the creatures flying over roads are lifted clear of the windscreen by a smoother slipstream.
On the whole though insect populations have declined, for many reasons.
@samueltyler2 Indeed, in fact more than upsetting it is potentially very serious for us.
One problem bees now face in Europe is the Asian Hornet, which has started to appear in Britain where it is officially notifiable. It is larger and a lot more aggressive than the native European Hornet, and its favourite prey is bees, hawking around outside hives to pick them off.
The bees are also susceptible to a disease called Varroa, carried by a parasitical mite. I don't know if it's still a serious threat or if honey-bees have started to become reasonably immune to it.
