Following the appearance of 15-inch models of the latest Retina MacBook Pro in Apple's online store for refurbished items over the weekend, 13-inch models have now debuted in the store, again offering discounts of roughly 15% compared to brand-new units. While a number of different configurations were available when the 13-inch machines first appeared late yesterday, Apple is currently listing only two of the three stock configurations as available with shipping estimates of 1-5 business days. - 2.4 GHz dual-core Intel i5 with 4 GB RAM and 128 GB flash storage: $1099 ($200 savings) - 2.6 GHz du