I did not understand the reasoning behind this until I read '16 man'. Sure if you are only running 16s and don't bother with tanks than I guess crit/surge and power outweigh ala. But in 8 man there are 2 tanks and 2 healers and I have to be as good at single target as the other healer. He may help me out or vice versa but primarily each is responsible for his tank. Alacrity at 8-10% really shines here.
though Force since it won't deplete anyway.
Even on 8 man raids its still fine because force armor eats up quite a bit of damage giving you more than enough time to top someone off. Plus when healing trance is criting for more than 2300 its more than enough to single target heal a tank.