Dear D.C.: It's nothing to fret about. It's one of those "many a slip 'twixt the cup and the lip" situations. There is a sequence of events that has to occur for a plant to bear fruit, i.e. reproduce. Interference with any one step can stop the process.
In this case, it's likely that the warm weather we had very early in the season caused the plants to bloom earlier than normal. Then a couple of hard spring frosts finished the flowers off. No flowers, no fruit.
The magnolias were a spectacular example. They were in full glorious bloom one day and the flowers were limp brown rags the next. The magnolias didn't fruit this year either, but most people don't notice magnolia fruit, which are odd and lumpy.
Another usual cause for failure to bear fruit is that somebody sheared the bushes and cut all the flowers and berries off some time in the last year. There are no future consequences unless someone pruned them all off again this fall. Next year's berries are already set on the bushes in embryonic form. Hollies bloom on last year's wood.
As you noted, holly bushes are dioecious, meaning that there are separate males and females. The flowers on the male bushes produce pollen. The flowers on the female bushes have ovules that when pollinated develop into fruit and seeds. Sometimes a holly won't have berries because it happens to be a male, unbeknownst to the gardener. Sometimes a female bush will fail to produce berries because there's no suitable compatible male bush nearby. There can also be a problem with the insects that do the pollination. It's complicated.
There's a long list of shrubs and trees that are dioecious. If the fruit is inconspicuous, it doesn't matter. A male and a female juniper are needed to produce juniper berries, used to flavor gin, various game meat dishes and choucroute garnie, the classic Alsatian sauerkraut dish. Blue-gray juniper berries are good for holiday decorations and for wildlife.
Bayberries are also dioecious. Bayberries are coated with a thin layer of scented wax that was used for candles in the olden days, probably mixed with tallow, which is very hard, highly saturated animal fat. "Bayberry" candles now are made of paraffin with artificial aroma, but they smell good anyway.
Some ornamental plants where females (along with a token male) might be preferred include fringetree, persimmon, yew and spicebush. Mulberry fruit might be desirable, or might not, depending on whose car is parked under the tree.
Carol T. Bradford, of Syracuse, has been gardening in Central New York for more than 25 years. Send questions in care of Home & Garden, The Post-Standard, P.O. Box 4915, Syracuse, NY 13221, by fax to 470-2111 or by email to firstname.lastname@example.org. Letters might be edited for space and clarity.