I have to disagree with this reasoning. Warriors also have no class features, but your Guard prestige class has the same BAB and HD as the Warrior.Changed the skill points. Experts have no class features...
The messenger I see as the NPC Prestige version of the Scout/Rogue/Ranger classes, which requires every bit as many skill point as a expert.
I also don't agree with the person who said more than a few ranks in climb/swim being more of a circus performer than a messenger. That argument can be made for Jump and Tumble, but I would expect the messenger to have ranks in Hide, Move Silently, Knowledge (Nobility), Knowledge (Geography), Survival, Ride, Swim, and Climb. That's 8 skills, not even considering a few ranks in Tumble and Jump, or Profession (Messenger) [a requirement for the class], or Diplomacy (useful when relaying bad news in a way that doesn't force you to hide), or Gather Information (for when you need to deliver a discreet message to someone who is harder to find).
The class shouldn't have enough points to max out all of these skills, but 6 points is pretty much needed to have a couple maxed with the rest being raised to lesser levels.