"Interrupts can only notify the microcontroller of events, they can't really be used to give you data, unless you are talking of Serial communication"

Don't confuse the isse!
You are right to say that an interrupt only notifies an event - this is true for all interrupts without exception.

With the 8051 Serial Interrupt, the event is that a complete character has been received and is available in SBUF, or a complete character has been transmitted, so SBUF is ready for antother one. Many other peripherals could raise interrupts to the processor to indicate that they have data available, or are ready for further data - but the principle of the interrupt remains the same: it just notifies the event; it does nothing with the actual data - that is up to the user to handle the event (interrupt).