...and the answers are fascinating. Campbell's officially says (on their US V8 site) that V8 is a blend of 8 vegetable juices, and calls it 100% vegetable. Which 8 vegetables, exactly? A great trivia question, and maybe good for winning a beer bet -- er, V8 bet -- in a Vegan bar somewhere. One of them is watercress, believe it or not.

On their UK Web site, however, they call it a blend of fruit and vegetable juices up front, but in the details they revert to "100% vegetable juice", with the same list of 8 "vegetable" juices.

Botanically speaking, the tomato is a fruit because it is a ripened mature ovary containing seed. There is apparently a horticultural rationale for calling it a vegetable, but as in all controversies, the lawyers had the last word: it was classified as a vegetbale in 1893 by the Supreme Court for trade reasons (imposing import taxes to protect growers).
Full disclosure: I condensed a bunch of Googled stuff for the last 2 paragraphs. I may be geeky, but I'm not that good.