Exactly the BrickPi is universal it can do everything that Raspberry Pi can do and it can do everything that the Lego brick can do.
Every platform has its advantages and disadvantages.
The Lego advantage is that it is super easy to built the physical robot, can can just clip it together anyway you want and if during testing you find you need to change the setup of the physical robot you just simply clip it apart and clip it back together in the needed configuration.
The Raspberry Pi advantage is it is super compatible to everything, it has every option you can dream of connecting to it and can run any Linux software. The Pi has USB, Blue Tooth, WiFi, GPIO pins, DSI connectors to the graphics processor, It will communicate with all the standard protocols like I2C, UART, SPI. So that makes it super easy for 3rd party manufacturers or yourself to make any sort accessory you can dream of to plug in to thebPI.