I wonder what's up with Season 1. I thought it might be a rights issue, but it seems the same company (Happinet Pictures) released both Season 1 and Season 2 on DVD. Maybe the Season 1 Blu-ray set just hasn't been listed on Amazon yet.
Then again, according to the Rokuga Jigoku blog, only Season 2 has been broadcast in HD on Kids' Station: http://catalina.blog.so-net.ne.jp/2012-10-03-5
No screenshots, so remember that just because it was broadcast in HD doensn't mean it's not an upscale. With King Records' track record, I definitely wouldn't recommend preordering this.