Probably because they were using Barnesdale limbs for a couple years. It appears that yours are Power Tuff limbs. Still, I haven't heard of many problems with them and I have yet to see a cracked limb like yours. All the ones I've seen were at the bottom of the limb forks. Did see some that looked like they completely delaminated. If you have problems in the future I think I'd either replace them and sell the bow or just bite the bullet and get Barnesdale limbs. Another option is to possibly strike a deal and see if Martin will replace them with the new Split limb technology if it's adaptable to your riser.
Thanks for the input. I do enjoy the nemesis very much and it is a great bow. I'm not sure what I will do if the problem occurs again. I guess I will cross that road if it happens. I haven't heard too many Power Tough limbs failing either and I thought it was odd that it cracked right on the limb bolt as well. Hopefully they will just upgrade to the split limbs with out asking. But I will keep you all informed as the issue gets fixed.
2012 Rytera Nemesis - Sword Twilight Hunter Sight - QAD HD Bone Collector Drop Away - WindJammer 7" Stabilizer - 438 Grain Beman ICS Hunter Elites - G5 T3's & QAD Exodus Swept Back Version