I believe like a lot of things in life, things change over time and you either go with it or you get out.
I have played almost from the beginning and have seen many many changes that have had a large impact on the game and each time it has led me to other games such as wow or FPS(games) or it has been a positive for me and kept me playing but doing something else or the same thing differently.
I'd imagine the people complaining are those that remember rs2 how it was and still holding onto that memory wishing it wouldn't change but also finding it difficult to accept the new change.
In my opinion there is no end in the near future for runescape. Stellar Dawn will be different to rs and a lot of players that quit to try it, will only come back because rs as it is now is closer to your pre-existing memory than a completely new game.
The same happens to WOW every time a new MMO is released. People will stick to what there used to and enjoy.