LOL, it's not paint. That is called screentoning, and shoujo manga titles often do this. It's part of the genre. Shoujo manga focuses on character interaction, rather than in making each panel look greatly detailed. Comics are supposed to tell a story, and sometimes, detail in a background isn't the most important thing.
I use Adobe Illustrator for the outlines, and Adobe Photoshop for everything else. I do it by mouse, so it takes me more than 8 hours to complete a page. I could say, more than 12.
But thank you very much!