Yah, but those drainage ditches are now called bio filters. Back in style, upgraded a bit.
Short answer - plastic pipe.
I agree with MY, too. There are more catch basins now.
Just as I started out on my own, the smooth wall interior HDPE drain pipe came on the market. I don't recall the exact numbers, but concrete or corrugated metal were standard at the time. the HDPE came in at about half the price, and because it's interior was smooth, flowed better. As a result, where you needed a 12" pipe in concrete (and 15" in CMP) you could use 10" in HDPE, further lowering the cost. At first, it was just in small sizes, but soon was sized all the way up to 48".
Architects realized it allowed more freedom and started designing drainage the way it could be done with the new tech. I recall one of my guys going to the Cornish/Graves golf design class. They said that drainage was typically $50K and my guys stood up in class and said we averaged twice that. Graves acknowledged that the "old way" was to open courses leaving a lot of problems for the super to fix slowly, but the trend would be to do more up front.
The sheet flow Mike Young mentions also got better. The 1970's standard was "shoot for 2% and accept 1.5%." That kept rising until we now shoot for 3%, but accept 2.5% as the absolute minimum drainage slope, and many guys don't accept less than 3%. I guess it was sort of a sea change from accepting some areas didn't drain, and grading just what needed to be graded to realizing that it wasn't that much more to strip the entire hole in anticipation of grading everything to minimum drainage standards, and while you were at it, this obviously opened up more design options, which were soon explored.
Of course, full loop paths had positive impact on construction of clay based courses, as did more sophisticated irrigation. Neither was developed for courses built in perfect soil conditions.........Lightweight mowers probably helped maintenance, too.
Of course, iconoclasts here can easily question what went on, but a lot of it was positive for putting golf nearer different population locales. The ODG designed in clay when commissioned to do so.
Bob, I am not sure siting greens has changed a lot over time. No one I know actually sites a green in a swale as its always dangerous to really disrupt drainage patterns, even if it is possible to do so.