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?



to remove the cap to get to the filter.
Along with easier to recycle.

)
