Okay, I'll bite.
1- as real-time as on your laptop, so that doesn't advance/disadvantage (given that you need net access, most ipads sold are wifi-only)."
That's assuming that someone has a laptop - if they've just got a desktop machine, then they can't lug it around. If they do have a laptop, they may not want to take it with them - for example, if some has a costly, well-specced 17" model that they use to earn their daily crust, there are a number of reasons why they may not want to take it on holiday with them.
No one – certainly not the reviewer of this app – is saying ‘give Photoshop, GIMP etc., the heave-ho, this is all you need.’ The beginning of the review mentioned about the popularity of the iPhone 4 being used to upload to Flickr, so I inferred that Mr Joseph was setting the kind of context of how people might use this app.
This type of app is a convenient, easy to use way of editing photos – although I’m sure you can do some impressive stuff, if someone wants to do heavy-duty editing, then they would do it on desktop/laptop. On the other hand, if someone was on holiday or backpacking and wanted to send some photos home or upload them to something like Facebook or Flickr, after a bit of tweaking, then this is going to be a good way of doing it.
Also, very importantly, touchscreens offer an interface that a conventional laptop or desktop. Some people may find being able to touch the screen to edit photos, a more pleasurable and engaging way than using a mouse or trackpad. This is something I think is very easily overlooked about tablet devices – they offer something that is not necessarily better, but different.