Actually, it's a recent policy change on AW's part. All(?) Epic Mage-Only cards used to have only one included in any particular set. But apparently players either complained, or (in a poll AW conducted back in early 2013) they indicated a distinct preference for having two of them. So, once the results of the complaints and/or polls were tallied, AW now includes two of pretty much everything in every subsequent set. Sets that came out prior to DvN were not changed however, for obvious reasons.
Upside: going forward at least, we can expect two of every spawnpoint (and other Epic/Unique/etc cards) in every new set.