This is definitely a trend on aircraft with newer seats. Even comparing the MD-88 to the newer seats on the MD-90: on the 88, there are two "normal" exit rows where the seats recline a bit and there are no fixed armrests. On the 90, there are four rows around the exit that do not recline, and some of them have fixed armrests.
My conspiracy theory is they are making the exit rows less comfortable so they can upsell to C+.