Yan 

11 speed cogs let you use a smaller chainring. By doing this you get a better low end which is desirable for touring, and you can still keep a decent top speed. When you change from 11 to 12 teeth on the small cog, you're losing a whopping 9% off your top speed. Now you are forced to use a large chainring which guts your climbing gears.

This doesn't make much difference in triples but with doubles it is a big deal. On a 22-36 crankset, the 36 chainring is low enough that you can use it 95% of the time. It is extremely convenient because you never have to touch the front shifting unless the road becomes very steep. If you got rid of the 11t cog, now you have to change that 36t large ring to a 40t. With a 40t chainring, you're now having to touch the front shifting more often, which makes the bike more annoying to operate.