PS Express lets you edit attributes of an image including lighting, colour, composition (cropping) etc. PS Touch gives you much more advanced functions such as layers. PS Express is a free online tool whereas PS Touch is a paid-for app that works from your device.
Thank you for your answer which is simple but accurate. Photoshop Touch is a
multi-functional editor and builder of graphics, and is capable of exporting its
output to Photoshop CS5 for further refinements. Like having Photoshop CS5 on
your iPad.... quite wonderful. While Photoshop Express is a simple digital
photo editor that works for everyday camera work. A very nice program.
BTW... Adobe Customer Service had me on the phone for over an hour, on hold and
off, and could not answer the question until they turned the phone call over to
a Supervisor in Tech Level 2. Very sad....