What ad said that?
Adobe has some other applications for phones and tablets (Photoshop Touch, Ideas, etc.), but the full version of Photoshop requires more horsepower than is found on a phone or tablet.
I have had a wee play with Express, but I couldn't take it seriously. RAW files tend to look outstanding straight from the camera when uploaded to an iPad, and it super easy to upload a card full of images and video. (Note I only have experience of the iPad 3)