Suffice to say they were very late in complying, and had to be reminded to comply. The SAE standard (SAE j1349) came out in 2004. Honda had to restate some cars as well but Toyota was the worst offender. Everyone else was in compliance in that timeframe - Toyota, Honda Dial Back Horsepower Claims
According to this little blurb:
About - Certified Power (SAE J1349 and J1995) - SAE International
The 2006 Corvette Z06 was the 1st car tested under the new standard, and the standard is/was voluntary.
Maybe the Japanese horses were a little weaker/smaller than their American or European counterparts (prior to 2007)
I'm not sure where you come up with "reminded to comply" or "offender" to a voluntary standard. If the Corvette Z06, a car that is sold on its perceived horsepower/performance, was on the "bleeding edge" being tested with this new standard in 2006 (model year), it doesn't seem too far fetched to me, that Toyota might take another model year to comply to the voluntary standard.