Adobe has always been trying to address the 'fat pixel' problem. In a previous app 'Adobe Eazel' they tried to solve it by generating many vector shapes to mimick watercolor on the ipad, but seems they also think it's not a good idea afterall so that ditched the app. You can take a look at this technical review http://www.expresii.com/blog/innovations-in-digital-painting-tech and see if you another approach Expresii uses to tackle the problem.