There are a lot of references on this show to WKRP being a rock & roll station and having a rock and roll format, but a lot of the posters on their walls are of non-rock artists and some of the music that Venus plays isn't rock and roll. I wonder why that is.

That was the main plot device. WKRP was all over the map, format wise, Johnny was playing oldies on a Top 40 station, Venus was playing soul music on a Top 40 station. On Sundays they had a former pro wrasser turned preacher, who smashed the stations vending machines for fun.

The station itself was like a character. Multi-faceted, never easy to pin down. This is what really "rocks" about KRP. I never really noticed the music. After they introduced "canned" laughter, I would only watch it with the sound turned off. much better that way.

It was considered a rock station but Andy was always asking Johnny to play songs from the top 40 list and that would have been soft rock, hard rock and even disco & possibly a little country music too.

The most likely person to had put up the posters would have been Andy,since the station was Top forty.Rock makes up the majority of Top forty,but there is so much more to it,thats what made late 70's and the 80's Top forty so good.
You would have Carl Carlton,The Eagles,Donna Summer and cross over country all on one station,and many times on mom and pop stations similar to WKRP.

I always thought Andy Travis was a symbol. An analog meant to represent the repressed "queerness" of the collective screenwriting crew. I thought it was a pretty obvious trope. Maybe it was his tight wranglers?