Blizzard has announced that at the start of Season 3, bosses will drop tier at a reduced rate (1:3) compared to previous seasons (2:2).
This means that for a Mythic raid, only 1 piece of tier will drop on Season launch (was 2 in previous Seasons). For a 30 player Heroic raid, this means that only 1.5 pieces of tier will drop on Season launch (was 3 in previous Seasons).
Here's a chart showing some examples of player counts and expected loot drops.
*Decimals indicate a percent chance of an extra piece of that type of loot. 1.5 pieces of tier means 1 piece of tier and 50% chance of a 2nd. 4.5 non-tier means 4 pieces of loot and 50% chance of a 5th piece of loot.
Note that this means that raid groups will likely now need 20 players in order to guarantee a piece of Tier to drop. Otherwise, there's a chance that no pieces of tier will drop with less than 20 people.