Not that unusual! When something new, or special, or unusual hits the street a lot of people want the 'latest and greatest'. (Smart was charging $100 just to get on the waiting list for a ForTwo!!) But, as time goes by without significant changes interest wanes.
I saw that happen with my Hemi Magnum. 2005, everyone was "Wow, what a wagon!", and "Is that the Hemi?". 2006 and 2007, no changes. 2008, discontinued! Still an excellent car, just as nice as 4 years ago, but gone!
I recently saw pics of the maybe future CTS Wagon. Looks like a customized Magnum without the Hemi!!
If GM does axe the XLR, it will only make it more desirable and exclusive for the lucky folks who own one! The 'classic' cars of the future will not be the million sellers of today!