Not true. Another example. Interactive does not clear all of its business in all markets. It owns the exchange seat, owns the hardware, does the execution, etc. At days end it just gives the trades up to the clearing firm who does the clearing for IB. In cases like this, the clearing firm has no responsibility for the brokers software, hardware, etc.
There are other cases where broker A will use IB for executions (IB via front end or back end software) and IB will give the trades back to the broker who does their own clearing.