If you progress through a career in GTW you can count on coming to work and finding that ALL of your coworkers have been culled and replaced at least once, and probably twice in the course of a career. I tend to treat townies as random/disposable npcs anyway, so I'm not that bothered by it. They mostly have negative/useless traits anyway. Some culling is necessary to avoid static games. It is nice to see new faces on occasion. I just wish the process was smarter, less random, and less widespread. The only time I care is when a townie that my sim is trying to romance gets culled.
You can save some of them by moving them into lots. I prefer to fill most of the lots with player created Sims. Even if I don't actively play every household, I'll have some un-cull-able sims to interact and build relationships with.
I'm more bothered by the multiple random romantic interests that my married Sims always seem to accumulate during rotational play. TS4 Sims are apparently not very monogamous. The absence of story progression is very noticeable in TS4. TS3 progression was completely broken, but at least it existed in some form.
Sorry, I realize this post is kind of random and off topic. :)