When Apple's Pro App for photographers, Aperture, hit the App Store, the price dropped from $200 to only $80. Compare this to Adobe's $300 Lightroom app.
Providing Pro Apps at such low prices helps to establish Apple's hardware as more affordable. Today's young computer users bring a sophistication to application utilization that previous generations did not. High school students quickly outgrow iMovie's capabilities in their media classes and are prepared to move up.
Forget "Pro Apps"- these are "Advanced Apps" and, though the pros may not like it, these apps are going to make it into the hands of amateurs and hobbyists.As a professional photographer, I recommend Aperture to even the most novice digital photographer- if you can understand iPhoto, Aperture is within reach.
Ultimately, don't let the low price fool you. Volume of sales and baiting eager pro app users to the Apple OS will do more for Apple than trying to make these apps solely available to professionals. Software-only companies are at a big disadvantage here- selling inexpensive (and great) software will ultimately increase their overall sales as the hardware flies off the shelves.