It seems to me that anytime there is a conversation about current vs. older shows, the point is made that because the clues seem to be getting easier, the contestants must not be as smart as the good old days.
I believe there are two factors at work here that get most of us into that mode of thinking:
1. We watch the show every day, and have watched for most of our lives, mostly from the time we were kids. Do I have a much larger knowledge base at age 39 than I did at age 11—yes I do. Do I have a larger knowledge base now than I did five years ago—I think so, by watching every day and playing other trivia games and reading all the time the extent of what I know continues to grow.
2. The evolution of the style of the questions given, not just on Jeopardy, but on all game shows is more a factor of keeping the audience watching, not because the contestants aren’t as good as in the past.
I think the contestants are every bit as good now as in the past, but the criteria they must meet for the shows has changed.
As far as the question for is it harder to win three games now or was it harder then, I think if someone has and can analyze the statistics of number of contestants each year that won three games, we may be closer to our answer, even if we continue to debate it.
Keep in mind that the current show has had maybe 10000-12000 contestants, only 329 have won $50,000, something that should be achievable in three wins with the current dollar amounts.