There's no hesitation on their part - they just jump right in and start in with the image pager class to handle the display of a number of images at a time. The files are stored in a directory on the local filesystem (as they should be) and pulling them in is just a matter of reading the directory. They integrate in basic back/forward and the ability to enlarge the images and the basic gallery is complete.
Now, it's time for the fun stuff - they take the processing that the PHP script was doing to grab the files/display them/etc and move it to the backend, replacing it with a simple Ajax call to another PHP file to grab the image information to display. They even finish off this part of the series with a method for implementing metadata for the images, an XML file with a summary of the file's attributes, date taken - anything you want, really.