This was known about the rMBP. I bought a regular Pro because of it, in part protest, in part for functionality reasons. People want the "shiny new" but the consequences are there for future product. If you buy them in droves they assume you like the limited aspect of future proofing. Besides most users say they never want to upgrade their laptops. They just buy new ones. If it makes you feel any better the SSD options for the retina are no better than the SSD Apple sells you. May actually be slower.
I'm not sure what they sell. But Samsung P830 is a great SSD (not the best as some seem to say) and top notch. Better SSD's would have a slight to possibly negligible performance increase. Although statistics wise they would possibly have an edge. The ones I am referring to are SDD's such as the OCZ Vertex 4, which has great specifications and there is no OCZ Vertex 4 or any other premium drive in the proprietary format so you're basically stuck in a rut.