Question about SDA/SCL settings in twi library

Using Arduino Networking, Protocols, and Devices
#1

I find it weird that the twi library pulls SDA and SCL up in init() like this:

  // activate internal pullups for twi.
  digitalWrite(SDA, 1);
  digitalWrite(SCL, 1);

instead of using the hardcoded/hardwired values for SDA/SCL (as they are used in transmit() etc).
This can lead to hard-to-debug problems.
The SDA and SCL settings don’t seem to be used anywhere else anyway.

Any explanations?

#2

For I2C (using the Wire library) pull-up resistors are needed to make the I2C-bus work. So the internal pull-up resistors are activated, although they are very weak (20k).

This is however a problem for 3.3V I2C devices, which can't have a pull-up to +5V. So the most common solution is to use 4k7 external pull-up resistors to 3.3V for 3.3V devices.

But I would like to have to internal pull-up resistors removed.....

#3