I feel like SourceTree actually only maps every Git command with a button, nothing more.
Contrast this with Github for Windows/Github for Mac. These applications are trying to make getting startet with Git easy. If you're using Git with a GUI, that's the way to go, not with a toolbar full of obscure buttons.
This is true - while mentoring at McHacks last weekend, I've seen more high schoolers and undergrads using GitHub via the app with a very basic understanding of how it works; some making sole use of 'Sync' button.
Once you're experienced and you need to use all the "advanced" features of git, SourceTree makes it easier to do so without having to remember every correct syntax without the fear of doing something fatal to your working commit (before pushing it).
EDIT: Not to mention, the integration with git-flow is just amazing for someone who wants a set work flow (pun not intended) and naming convention without the extra overhead of thinking about how to manage it.
Anyone more than the simplest app with only one developer will quickly require more than what the GitHub app provides. Whatever issues you run into, when you Google and you haven't learned git, you'll have no clue. I like the mapping of git commands: I can use the CLI, but I have a tool that makes that workflow faster, rather than hide it from me because it's too hard.
However, for a tool that lets you quickly commit and push, which is what the Github app is ideal for, Gitbox is very nice (Mac only however).
SourceTree is that app: you know how git works but you don't want to fiddle with CLI commands and text output limitations. 99,5% of the everyday workflow is covered by a nice GUI.
Alas atlassian decided to go after the "Github App - no clue of git" population by "simplifying" the UI in 1.9. It's my impression that that move backfired hard in the existing SourceTree user-base.
To be fair, I haven't used 1.9. These days I'm mostly in Tower, which felt like SourceTree with some added features (the way it does stashing is pretty nice)
Yes, but you can do a lot more with SourceTree than with Github app (last time I tried GH, anyway). SourceTree allows you to do some pretty involved things, and because of that, it has to be a bit "closer to the metal". It's still very easy to do the basics IMO, but you do need to know a bit more of git terminology, etc.
Different target markets, IMO.
I don't know many serious devs that use the GH app, to be honest (because of its simplicity).
Contrast this with Github for Windows/Github for Mac. These applications are trying to make getting startet with Git easy. If you're using Git with a GUI, that's the way to go, not with a toolbar full of obscure buttons.