There are 2 other reasons to favor triggers though:
1) People (Josh Drake comes to mind) have found that if you get over a tiny number of partitions, the performance of rules is abysmal.
2) I believe it should be possible to construct an update trigger that allows you to perform updates that will place the row in question into a new partition. While I can see cases for simply disallowing updates to the partitioning key, I think there are also times when being able to do that would be very useful.
The consensus seems to be veering towards triggers.
I think it'd be great to make adding and removing partitions as simple as ALTER TABLE. I don't think that DELETE should be the mechanism to drop a partition, though. Again, DML statements shouldn't be performing DDL.
Since partition is inheritance-based, a simple DROP or "NO INHERIT" will do the job to deal with the partition. Do we want to reinvent additional syntax when these are around and are documented?