Serial inputs and outputs

I have two ARM processors and the TXD and RXD serial input/outputs are said to be an rs-232 connection or w/e it is required to transmit.

I just do not see the point of using an rs-232 DB9 connector to even transmit the information. here's the question, should I be able to just connect my Transmit out PIN from one ARM Processor to the Read in PIN of the second ARM processor?

The way it will be set up is a one sided input and output

[ARM1] ---> (TXD serial out) to (RXD serial in) ---> [ARM2]

please explain why or why not it would work.

thanks