@Hinscher:
at both arabasta and skypiea Robin was annoyed because they were both weapon locations
then on skypiea she commented how some showed wapon locations while others had history
I recall Alabasta differently, though admittedly I'm going off the Viz translation here… Robin lied to Crocodile when they first allied to eventually get herself near enough to read it: she was interested in the "history" aspect, but told Croc it was the location of the Pluton because she couldn't get to the poneglyph on her own.
When Robin explained that it contained only a historical record, Croc was understandably angry, but I think Cobra's reaction was more telling here: he was confused, wondering something like, "Why would we be hiding history?" (Don't have my books with me at the moment, so again, grain of salt).
Then, with Water 7 and Enies Lobby, it is revealed that the World Government does indeed have a vested interest in keeping history in the dark, making the idea that Robin wasn't lying when she said Alabasta's poneglyph only contained a record of history quite plausible. Robin's annoyance at Alabasta was therefore due to the fact that the poneglyph contained known history, as opposed to a record regarding the Void Century, which is what she was really after, not that it was necessarily truly about the Pluton.
That's my view on it, at least.
As I said before, though, I'm completely omitting the Skypiea poneglyph at the moment, since I don't recall what was said in regards to it, save that Roger left a message there…