Classic "assets" pose.
They don't really sound the same. Nozawa does each voice differently, even Goku and Gohan have slight differences in the way they speak.
Masako Nozawa was handpicked by Mr. Toriyama himself. The reason she was kept even after Goku's growth spurt in the 23rd Budokai is that...well, it was never an issue.
http://www.kanzenshuu.com/forum/viewtopic.php?t=28292
To be fair Luffy (who shares a voice with Kuririn who's voice also didn't change) Naruto's and voices never changed either and they're also voiced by women. Female actors voicing adult male characters is a common practice in Japan.