70 mm (horizontal) (IMAX DMR blow-up) (Kodak)

[in2video2]

I've noticed that many of the new IMAX presentations in the end technical credits include the credit:
70 mm (horizontal) (IMAX DMR blow-up) (Kodak)
Wondering if a few of our technically-minded forum members may be able to help me out with an explanation of what this means. Star Trek (2009) and 2012 (2010) are two recent examples. I am thinking this means that the original 35mm Panavision film stock is blown-up to make a 70mm Panavision master which is then used towards the final IMAX prints which are then distributed for presentation. Original Aspect Ratio for IMAX is 1.44; 35mm Panavision has an Original Aspect Ratio of 2.35 or 2.39 and the 70mm Panavision would have an Original Aspect Ratio of 2.20.
Might be wrong here but wouldn't it make more sense economically to shoot in 70mm (65mm negative) to begin with? Wouldn't the quality be better, too? And the end result for us, the Blu-Ray consumer, wouldn't the image be more impressive? Seems to me we are seeing the 70mm catalogue releases being systematically short-listed and rushed to Blu-Ray with impressive results. Hope someone can bring me up to speed on this. Thank you.