I think it's because of the lease agreement time frame they put 10-12 years, of course the air frames could be used much longer.

I'm hearing rumors EK's UK bookings have dropped around 10 percent since the Brexit vote, they say China is also experiencing a large decrease in bookings. Can any body confirm this, I asked for confirmation somewhere else but I'm still waiting.

Any way if this is the case EK would do just fine with the 777-10 in the future.