Yea, just look at most other MMOs that recently came out, RF Online, D&D Online just to name a few. The retail box prices all dropped within just a few months of release, yet WoW's retail value just dropped from $50 to $40 after more than a year since its release.
And especially with the BC expansion coming out, it certainly makes sense to drop the price down to $30. WoW is just too addicting. I for one have quit after decking out my Paladin with bwl epiX... I just don't care for AQ and whatever that new instance is.