"What if Greenland was at the north pole 15,000 years ago? The cold would have kept the Greanland area frozen to fit the model. And it's opposite pole would have been in the southern hemisphere ocean, which would have melted w/o a trace. This suggest a polar shift has occured in the past?"

This is good point, that I didn't think about, nor apparently did the writers of article. As it is known the North Star moves in your sky in the time frame of thousands of years.
"The direction of true north is marked in the skies by the celestial north pole. For most practical purposes, this is the position of Polaris. However, due to the precession of the Earth's axis, true north rotates in an arc that takes approximately 25,000 years to complete."
http://en.wikipedia.org/wiki/True_North

How much does this move?
"During the last hundred years (27, 28), the north pole of rotation has wandered 10.81 ± 0.03 m towards 79.2° ± 0.2°W"
http://www.pnas.org/cgi/content/full/99/10/6550

So, just get vague idea here. let's take 1/2 of 25,000 [12500] divide by 100. 125 times 10.81 meters equals 1351.25 meters [which is utterly insignificant].
Hmm.
"The magnitude and direction of the secular trend unbiased by the presence of harmonics in the data were determined, yielding a rate of polar wander ~3.52×10-3 arc sec/yr (which extrapolates to ~0.98°/m.y.) in direction 80.1°W longitude."
http://adsabs.harvard.edu/abs/1981JGR....86.4904D

This doesn't seem like much either.

Obviously, the explantion given in article is much simpler and until such time that more is known about the history of polar wandering, I'll prefer the explanation of gulf stream being blocked- at least as the major factor.