No, just common sense. 
They either never put any thought into weight limitations for quadruped flyers, or figured it wasn't worth worrying about. Just like they didn't mention that a centaur doesn't get any benefit from those extra legs of his when he's climbing up a rope.
Obviously, the designers wanted the Pegasus to be able to carry a Paladin. I'd just prefer to invoke some common sense and put that Paladin on a diet...
They either never put any thought into weight limitations for quadruped flyers, or figured it wasn't worth worrying about. Just like they didn't mention that a centaur doesn't get any benefit from those extra legs of his when he's climbing up a rope. Obviously, the designers wanted the Pegasus to be able to carry a Paladin. I'd just prefer to invoke some common sense and put that Paladin on a diet...
