Does RIM set the prices on App World? I would imagine they set baselines, but devs set the prices. Typically apps will be more expensive on less popular platforms like Blackberry OS and Windows Phone because devs need to charge more in order to recoup development costs which they could make up on volume on Android or iOS.
$650 was not an especially unreasonable price for the 9900 when it launched. I probably would have tried to place it at $599, but I don't know their margins. The device represented the flagship model of the Blackberry brand. If RIM were to price it at $450, for example, they would be devaluing their brand, as well as making it difficult to create differentiation from the Curve series.
Their flagship models need to continue to be priced similarly to flagships from other brands, which means $150-200 on contract (since the market for buying premium devices outright in North America is small). However, they will definitely need to follow that up with some lower-tier models around $0-50 on contract in order to get them into the hands of teens, students, and prepaid customers.
RIM doesn't have the cache to release only premium models like Apple, but they also don't want to be stuck with a reputation as a discount phone maker either.