This is a classic optimization problem, with the caveat that what's optimal for you may not be optimal for me. Though there are single-speed devotees, most roadies would agree that optimal is not below 8. Where's the sweet spot for most easily finding the right gear to spin without too much added complication, cost, and weight? For me, me I notice big gaps with my 8 speed Sora, which sometimes causes me to seek something better by switching chain rings, but that seldom happens when I ride my 10 speed 105 or DA bikes. I don't feel the need for 11, but if I rode it all the time, i can imagine I'd notice the advantage of having that extra gear - particularly adding a great hill climbing gear that I'd seldom need but would occasionally appreciate.

But let's put it a different way - how many cogs would you want before you'd be willing to do away with the FD altogether? Say you had a 16 cog cassette going from 12 sprockets up to 35 or so and just one chain ring? Would that be just marketing, or a real improvement? OK, so maybe that doesn't seem feasible, but one day....