Perhaps in road racing, but on the street? For me the point of riding a road bike fast is doing it with smoothness and safety. This means a V Twin (or a boxer for that matter). Smooth lines come from smooth power bands and lots of midrange grunt to pull through long sweepers while you're hanging off the bike. For this, in-line 4's just don't deliver like a twin.
Sure in-line 4's are fast in the straights but who cares? On the street I am not racing anyone- I'm thinking about how well I'm connecting with the bike, my line, and how smoothly I am putting it all together. Again if I were worrying about weather or not I had selected the right gear or weather or not I was going to DOUBLE my horse power over the next 1000 rpm's (possibly leading to a crash) I would not be enjoying my ride in the mountains and canyons and would only be able to have fun "punching it down the straight away" (to me not that much fun, certainly not as much fun as I am having on my twins, and even worse for loosing my license).
Handling aside, V's allow a more narrow bike combined with a favorable center of gravity translating into a more responsive machine. Perfect for what I like to do when risking my license and life on the street. If my 999 is not fast enough down short straights where I routinely hit 120+mph before leaning into the next corner, I'll pick another sport. If Johnny Law clocks me at triple digit speeds this game is over for me and triple digits is the only place where an in-line 4 has anything on my Duck, or Boxer Cup for that matter. I love my 999's razor sharp handling, quick transitions through the S's, and immediate response to even the most minute inputs- incredibly visceral while committed to the long sweepers, and tight transitions of my local mountain roads.
Viva the twin, the king of road going power!