Yes, iridium is supposed to be superior to platinum because it has a much higher melting point (2450 degrees Celsius) and is 8 times stronger.
The main benefit of the iridium plug is the long life and more efficient spark. Something to do with the much smaller center electrode having less 'spark jump'.
Of course, this is just what I've read.
Some claim there will be a performance boost for the engine (and even fuel economy), but I've found that the only real difference seems to be ease of starting.
In addition to NGK, Denso makes iridium plugs - the IUF22 is the one for the agility 50.