I think I've cracked the case of the Huge Zucchini Plant with No Zucchini!
The soil I had so industriously and regularly supplemented with 10-10-10 fertilizer may actually have had perilously high nitrogen levels, which prevent the formation of fruit! (learned in my gardening class, supported by multiple Google searches) Huge leaves, but no fruit. Two summers in a row. Two summers of the same fertilizer, industriously and regularly applied. Two different zucchini transplants, two others planted from two separate packets of seeds... and when they weren't growing, I added more fertilizer. The common denominator? The soil.
Step one is not adding any more of that 10-10-10 fertilizer! Then checking the results of the soil test to see what other things I may need to do. My hypothesis at this time is that the pH of my soil is high, which would indicate high nitrogen levels (I think).