I'm not sure why there's so much discussion in comparing the two. RDR is literally GTA: Wild West without the overly exaggerated and satirical social commentary.
Also, the notion that Take Two and Rockstar are somehow adverse to internal competition doesn't make much sense. Sure, it makes sense in terms of market cannibalization, but given Rockstar's tendency to value quality over quantity, it's evident that internal competition improved their games over time. For example, things such as bullet-time, assisted aiming, weapon wheels, mini-map elements, button-mashing mechanics, etc. Each successive game is a chance for Rockstar to learn what worked so that they can incorporate those new elements into future games. Whether it's GTA, RDR, Max Payne, or LA Noire, they all have a little Rockstar DNA within them; it's noticeable.