Makes no difference to me when buying and selling. I think it would have to do with the pops of the coins, that effects the price the most. And I see many more NGC 70's then PCGS graded 70's.

Therefore, many people perceive PCGS to be stricter due to lower pops. Thus the plastic (coin) they are buying is percieved to be rarer, and commands an higher price.

Really who cares about an MS70 vs MS69. Please tell me the difference. Point it out with photos. I often times hear PCGS won't cross NGC 70's cause they cant see the rims. Well once its in plastic no one else can see them either. So buy the 69 or 68 and be happy and save money.