Pat,
I suppose its a combo of both crutch, fad and necessity.
You mention Seminole. I recall playing there with Pete Dye and him mentioning he has no idea how it drains, but it does. I would say modern architects are more inclined, via experience, NOT to just take the chance that a low lying site, even with sandy soils will surface drain by itself. BTW, there are some surprising courses, like Prairie Dunes that also have a shallow water table problem to work around.
Ian's post is right on. Besides needing the dirt to raise fw, housing, etc., a predetermined distance above the water table, it is usually necessary to provide the lowest possible drain outlets at the nearest possible points on all holes, which is best done by long linear lakes paralleling fairways. If the water table is only a few feet below, it limits how far you can cut a drainage swale (probably to zero, as you have to recall that a water table varies and can be higher in the spring, at the highest Florida play season) so you need to limit the length surface water and even pipes run. But, pipes can run as low as 0.25% whereas good surface drainage requires 10X that. And, I suspect that most older courses in this situation have miles of French drain to correct the problems over time, not a possibility in this day and age.
Lastly, those ponds probably provide storm water detention and maybe cleansing for the entire development and possibly the region, as sometimes new developments were required to make up for shortages elsewhere, a factor not likely legislated when Seminole or Pine Tree were built.
So, call it a crutch, or whatever, I call it higher engineering standards and more regulations than we saw in the Golden Age.