In Diamond and Pearl, only 61 non-legendary, not-evolution-or-pre-evolution-of-an-old-pokemon were introduced, so this is not that bad actually.
I don't know why some keep using this argument. It doesn't matter, a new pokemon is a new pokemon, you don't need to be so random to justify your opinion.
Well, I for one didn't feel like there were too few new Pokémon in Diamond and Pearl when I played them, but when I heard the whole "omg noez only 70 new Pokémon in X and Y!" I was a little disappointed. However, Gen 4 shows that you don't need a whole lot of new Pokémon to be awesome.
3DS FC: 5026-4968-1695, Name: Adam Perfection is at hand! I have been made compleat.