We need a cucumber expert to step forward here!
I know that there are two types of cucumber. One type has both male and female flowers on it and one only produces female flowers (F1 types are usually the latter). If you have ones that make both types of flowers I know that you are supposed to remove the male flowers before they get a chance to pollinate the female ones, otherwise the cucumbers turn bitter. (There is a feminist message in here I think).
I don't know enough about the sex lives of cucumber plants to understand how a female-only plant can produce fruits that, as they are unviable, don't just drop off, as any other plant's fruit would do.
Do you know the variety of cucumber you have? Have you seen flowers with little mini cucumbers behind them and flowers with no mini cucumber behind them on the same plant?
Not much help in answering your question, but someone else may be able to pull it all together for both of us!