It's a matter of OOP modeling. Object methods are better reserved for performing actions with side effects, or complex logic or calculations, and not for getting state or simply setting public properties; and as a caller, I don't really care about the implementation details of (in my above example) getting the last forums post, I just care that it's a property I can access. (Maybe it came from a cache and not the database? Maybe it was set earlier in the script? I don't care.)

Putting it behind a getter doesn't "hide" control flow. It just makes for a cleaner interface from the caller's perspective.

FWIW, I almost never use setters. Getters are are much more useful, especially for lazy-loading basic properties.