I can only guess here - maybe (server) space is an issue here - instead of redistributing all identical packages for each SP, the "old" packages seem to get inherited from the previous SP.

Unfortunately, I have no further insight into this topic yet and even find the TID inconsistent ("SLES11-SPx-Pool : This is the unpacked installation media, all binary RPMs from the actual installation media. It never changes once SPx has been released." - but there's no "SLES11SP2-Pool" in the list...). Confusing, at least.