This is the exact reason I started using it 4 years ago, I haven't used other CMS platforms other than Sharepoint (which is a whole other kettle of complex fish).
WordPress isn't perfect, though neither is any other system, but it's good for clients out the box, the editor UI is similar to Word, uploading is pretty straightforward and everything is fairly clean. Combining it with something like HTML5 Boilerplate means I can have a basic frame ready in a day or two, drop in my loop, some wp_nav and I have a skeleton ready to go with navigation.
The hard part is finding reliable plugins, but this comes with time. I now have a "go to" list for tables and forms, and I'm working on security hardening next. Once I have set of core plugins I can get those up and working in a few hours too.
I want to work on a way to inject pages into the MySQL db next, I can get Dreamweaver to create basic formatting markup (it's still good for something!) and then I want to find a way to mass upload it all into the db with all the correct entries, it would save me loading each page individually to copy and paste for reams of content. It may be a huge waste of time, but I've had to populate WordPress sites with 100's of pages before and it's not fun, Sharepoint was waaaaay worse 6 years ago though!!
You can get a website to do anything regardless of the platform it is developed on, just different amounts of effort and for most sites WordPress works fine if you put everything together correctly. Any PHP you learn for it can probably be reapplied elsewhere too and if you start dabbling in plugins as well, then you can probably do 99% of things quite quickly.
I find it's pretty flexible but then I design/develop with it in mind, I shy away from e-commerce sites but I'm looking to go into that soon too.
I can't think of a site I couldn't use it for but then I haven't built every kind of site at every scale
But I will take a look at the competition sometime soon too.