We kicked around the whole methane ice having one less picture thing a year ago. Yes, they have one less picture so yes,
on average the is a sligthly lower chance for methane ice worlds. But it really is meaningless in game terms. The difference isn't significant enough that it shows up noticably in individual games. Probabilities are only useful over a large sample size, and all that matters to us in a game is what's going to happen in this specific game. Even with a huge quadrant with hundreds of systems and thousands of planets, it's not really important the total number of each type. All that matters to you is how many of those planets are near you and that can't be predicted at all. Because of the randomness of placements and whatnot you could easily end up in a start system with a couple ice methane worlds and you'd be kicking youself for not taking it then.
As far as empire setup goes there is really no basis for choosing between rock or ice over other than personal taste or role play or whatever. The choice between Rock/Ice and Gas Giant does make a difference, but that's not to say one is better than the other. They simpley require slightly different strategies as Gas players will tend to have fewer but larger, and presumably better defended planets, while a rock/ice player will have more planets but be more widely dispersed.