It's interesting what specs manufacturers believe will help them sell product these days. In the 1980s those distortion numbers would be seen as horrible. BUT, the STRH190 owners manual provides additional information:
Minimum RMS Output Power (8 ohms, 20 Hz – 20 kHz, THD 0.09%) 90 W + 90 W
So 90 watts both channels driven at .09% RMS, not bad. I believe .03% is Amir's measurement standard, but .09% is probably not audible on music, if it is accurate.
BUT, the Sony webpage marketing folks chose the 100w spec even though it is 10 times more distorted. Because everyone needs 100 watts, right? It probably looks better on the Bestbuy tag.
Its not too surprising these value priced components are advertised this way, what surprises me more is the number of higher end components that are too.
Example:
PSAudio Sprout 100 ($599)...
4 Ohms: 100 watts per channel, both channels driven (no distortion spec given) and
THD Speaker Output: <0.01% -1W, 1KHz into 4Ω... (at 1 watt 1KHz? that certainly reflects how I listen to music)