I feel like that tells us something more reliable...But the fact that there's no 1300 or 900 or 500 values just makes me think that an odd numbered base conversion wouldn't make much sense.

It's fairly normal to have in game currency not properly align with real money. Let's pretend $1=400 shards. The cheapest item is 500 shards and the minimal amount of shards you can buy with real world money is 1000. To buy that 500 shard item you still need to buy 1000 shards and at the end of the transaction you're left with 500 shards. Now you either leave that 500 shards alone, or you buy another item, or add more money to get a more expensive item.