Why smartphone IR system uses an IC instead of GPIO?
"IrDA" is a somewhat more rigidly defined standard than "RC", including:
 (a) IR intensity / sensitivity vs. distance &amp; speed
 (b) limiting IR pulses to a maximum length (regardless of what the device
driving the IRED might try to do, deliberately or inadvertently)
&amp; (c) a 3/16ths encoding scheme, which an intermediary 'Endec' chip (e.g. MCP2120) or an endec module within a UART within a microcontroller (e.g. MSP430F5510) will do for you.

This is most easily achieved with an 'all in 1' module (without the endec) like this, for example:

http://rohmfs.rohm.com/en/products/databook/datasheet/opto/irda_module/rpm841-h16.pdf

Meeting all these specs in bit-banged GPIO when your CPU likely has better things to do is painful.  Using a UART, optionally an intermediary Endec chip, and an integrated IrDA module makes implementation much easier.
"RC" is different, less stringent.