I imagine we've all heard the old saying about "When the only tool you have is a hammer, then all problems start looking like nails." I am a longtime advocate of separation of data from presentation, and I think ProcessWire's templating approach is really cool. That said, however, there are a lot of times when it isn't practical or worthwhile to make much effort to separate your data into a bunch of separate fields and a template and then put them back together.
If I am writing a journal entry I may want to write a paragraph, insert an image inline with the text, write another paragraph and embed a Youtube video. I don't want to create a new page type with a text field or two, an images field, a movie field and a template to put them all together. I just want to sandwich some html markup with a header and a footer and move on.
ProcessWire is amazing for handling situations where you expect to manage a lot of repetitive "pages" (data structures) of a given type. For lists of skyscrapers, villas or lists of just about anything this CMS is the bomb - honestly it is amazingly clean! It's a little less clear that it is worthwhile to use a "template" approach when you're just making a one-off page or content block. Not all web content needs to be reduced to an abstraction of data and template before you can use it - this is the hammer issue.
Even if you load the images in a journal entry into the images field of a typical page template, how are you supposed to access them from within your rich text or markup? A lot of content doesn't need to be set up for easy re-use, it just needs to be conveniently used once. This is where I'm struggling a little. All in all, I think the ProcessWire approach is fresh and powerful, but it would be good to be able to put some images and scripts on the filesystem and discover that they are available below "/site/templates/mystuff".
One of my competitors is Salesforce's Desk.com, and they have an outrageously good sales website. A site like this would be really tough to develop in ProcessWire since almost everything on the site is handcrafted, single-use content. Not much of their site is well-suited for templates, but the whole thing is pixel perfect. There's a place in the world for content that isn't generated by invoking a template on a set of page data.
ProcessWire is an awesome tool, but not all content is so rigidly aimed at separation into data and templates. Some content is just content, use it once and keep moving. Lots of other CMS's make that easy, but they don't excel at the structured repetitive stuff like ProcessWire does. It would be great if ProcessWire also made it easier to produce those conventional throwaway pages, too.