Why the dig at MS Paint? I'd say the exact opposite: it's a simple pixel-level bitmap editor, and for that purpose served me well for years before I moved to OS X.
I must poke around Preview later to see what it can do.
Preview allows you to resize, crop, rotate and save images in different formats. (It is not possible to rotate in less than 90° increments which seriously sucks.) It also has nearly the same adjustment tools as iPhoto (exposure, saturation, levels, …). You can add arrows, ellipses, boxes and text to images (in order to annotate them).
That seems like the perfect feature set to me, I’m not aware of any situation where I actually needed to manipulate the pixels of an image. Cropping, resizing and saving in different formats is the most important functionality to me and in that respect Preview seems much more useful than Paint.
I actually never really need pixel manipulation. Tools like Lightroom are perfect for editing photos and I don’t see any need for Photoshop or similar tools at all if all you want to do is edit photos. The only time I actually needed Photoshop was to create bitmaps for a website (rounded corners, backgrounds, …).
(Preview also allows you to edit PDF documents. You can crop pages, delete or rearrange them, or easily merge pages from different PDF documents into one, all just by drag and drop.)
Who does create images? I’m pretty certain that the overwhelming majority of people do not, hence there is no need to include a drawing program with an OS. Cropping, resizing and adjusting photos is plenty for most people.
I create images because the inclusion of Paintbrush then MS Paint in Windows gave me access to the enjoyment and skill building to do so when I was growing up.
Indeed, I used to love MS Paint when I was using Windows on a daily basis.
It's simple, fast, easy to use, and does its one thing very well.
It wasn't until Paintbrush 2 came out that I didn't have any individual software from Windows that I missed when using OS X. I've never tried Pixelmator however so that might be a better replacement.
I must poke around Preview later to see what it can do.