It's amazing that people are still able to reach these types of conclusions. Reminds me of the time when people said that PS3 has better CPU and 360 has better GPU, ergo, PS3 games will have things like better, physics etc AI and 360 games will better graphics, particle effects etc. It was such flawed blanket statement born of distilling certain specification to fit conventional wisdom. It's the same thing now. Multiplatform games won't make reservations for both hardware either way and so there will be distinction. Devs will make whatever game they want to make and will take different routes to achieve the same goal on both platforms.
Also, neither 8GB nor 4GB (if indeed true) are fully reserved for making games.