Tomatoes are vegetables: It’s the law
The debate goes back at least to the nineteenth century, when no less an authority than the U.S. Supreme Court asked the question: “Are tomatoes fruits or vegetables?”
This question was presented after a fruit importer argued that since tomatoes were fruits and not vegetables (which were subject to a 10 percent import tax) they should be taxed as fruits (which were not taxed).
Though the Supreme Court acknowledged that, botanically speaking, tomatoes are technically fruits — in botany, “fruit” simply refers to the seed-bearing structure of any flowering plant — it was decided that they should be taxed as vegetables based on their most common culinary uses.
Source: The Daily Meal