How is it fair that PCGS coins sell for more than NGC coins?

Recently, I have looked at auctions with teletrade and noticed that PCGS coins seem to carry a significant margin in price over NGC graded coins. I was already aware of this, but just not to this extent. The 2005 MS70 Marine Corps commemorative graded by NGC sold for $150 in one auction, while the same coin graded MS70 by PCGS sold for $1,100! I feel that this is just absolutely ludicrous. I cannot believe that collectors will pay so much more for a PCGS coin than an NGC coin. Although PCGS may be just a little more conservative when assigning grades of 70 than NGC is, I still do not believe that this enormous difference in price is right. Collectors need to realize that both companies have their flaws, and that because of those flaws, should not pay such an extreme difference for a certain coin graded by a certain certain company.