My money is on making it harder for the do-it-yourself crowd to.... do it themselves.
It's real easy to find and remove a spin on filter, climb under the car and twist it off. To change a cartridge though you have to locate it, could be anywhere, and then have the right tool to open where it sits. I know on my friend's Cavalier it took an 1 1/4" socket to remove the cap to get to the filter.
How many people do you know that have one of those just hanging around?