This isn't accurate.
Which runs (marked or unmarked) at Plattekill are steeper than the upper part of Lift Line Glade (under Tomahawk), Chippewa, or some of the other areas at Belleayre? I'm not intending to be antagonistic, I would just genuinely like to know since like I've mentioned, I've only skied Plattekill once.
My thoughts are that while Plattekill definitely offers a much longer sustained pitch on most of its expert runs than those at Belleayre, the actual steepness of most expert runs at Belleayre is greater than those at Plattekill. For example, skiernet.com lists a 30 degree pitch for Yahoo's headwall versus a 21.7 degree pitch for Freefall: http://www.skiernet.com/9/angle-of-ski-trails.php