It's really a simple reason. The people taking the class only wanted to "correct" the images that came out of their cameras. Nothing fancy, nothing tricky or cute. Just crop and correct the images they took. The answer to that problem is Adobe Photoshop Lightroom 4 (LR4). It's actually simpler than PSE and the list price isn't that much more than PSE. $99.00 versus $149.00. When LR4 was $299.00 it was an issue telling people to spend three times the price. At a fifty percent premium it isn't prohibitive.
LR4 is totally nondestructive. PSE has the ability to ruin the image. LR4 has better database functions than PSE. Right across the main screen of LR4 it has all the options for what you might want to do with your images. Do you want to Develop (enhance) the image? Do you want to make a book, a slideshow or make a website? It's all there, right across the top.
Is your image to dark? Move some sliders. It really does matter which ones. You're not going to hurt to file. Does it look better? Good. Does it look worse? Move the slider back (or back so far you go in the opposite direction. If whatever slider you moved didn't help, move another one. There's a Reset button on the bottom right. You can always get back to where you started.
LR4 is understandable. You, typically, don't have to know that you can right click on an icon and bring up a whole expanded world of options.
Finally, you can start out on day one and get a feel for the program. As you progress, you will learn more and more about what LR4 can do. But, fifteen minutes in on day one you can make corrections to your shots.
Rather than take several weeks of classes for PSE, I could have the students in and out in one hour on one night with LR4. It's just that easy (to get started).