I think it is important not to take Rowl too seriously... He definitely makes an impact on the plot and we get a sampling of cat culture, but on the other hand we have him making rather silly observations about hats and the masts of ships being trees...
I think the hardest thing for me to work out is figuring out the relationship that cats have with humans. You have cats wearing spurs, a human invention made specifically so cats could be more capable hunters, but at the same time I am not even sure if everyone is aware that cats can speak and are intelligent. Bridget is the only human we ever find out can talk to cats that I can recall... and given the cats lack of interest in human affairs she is probably one of a handful of people who even care to. The only people who seem to take any interest in the cats is the Verminocitor's Guild, and they apparently kill cats.
Also I saw it mentioned on here somewhere that cats had thumbs, but I recall no description of cats looking anything different than modern housecats. They would kind of have to have them in order to put on those spurs, right?