Forum

Here's a more technical explanation:

The 802.11g signal when amplified higher than 30 mW tends to produce too high "out of band" emissions (bad interference causing signals). Therefore, in order to keep these out of band signals (emissions) at an acceptable level (for FCC certification) the power is dropped down to 30 mW.

It's less about what output the radio has than the link quality and speed made available. The radio at 30mW for OFDM has better performance for a given range than operating at 100mW for DSSS, and generally higher speed everywhere with much better bit recovery.

One final point is that the FCC has historically placed lower limits on radios with variants of OFDM as the spreading technique; however generally this has not been to the detriment of the radio performance (see above).

Hope that helps,
Joel