I2C and Arduino questions

The schematic for the I2C wiring shows the necessity for a couple of pullup resistors. Do I need to supply those or are they included on board?

I2C appears to be a multi-drop network (eg., multiple slaves accessed via addresses). I see several I2C enabled boards available. But once one is used/installed there are no connections left for board number two. Is that just my imagination or is that what how they are supplied?