DO NOT EXPECT HEALERS AND TANKS TO DPS!!! That is not their role. Tanks are the meat shields that hold the aggro so that the boss doesn't decide to try eat the beatsticks that you are, and healers generally make sure everyone is topped off and provides some group buffs to help with DPS and damage mitigation. If the boss is like 10% or 5%HP expect both tanks and maybe 1 healer to DPS to burn boss down.
EDIT: For you STR tanks that may or may not lurking on DPS forums, this also directed at you... You know who you are... Also if you guys communicate with your group to reach an understanding of what to do in fights you know how to do good for you.