Id have to disagree with the statement "If mods prolong the lifespan of the previous titles (e.g. MTW, RTW and M2TW) then that's a bad thing for CA who obviously want players to move on and buy the newer releases." Im of the impression that people who play mods buy all the totalwar games unless the game is not to their taste at all which would have nothing to do with modding.
Its actually a healthy thing in my opinion to have the ability to mod as it keeps the community buzzing and fresh, generating more interest in the series. For example some players would not normally have looked at totalwar but got it to play the excellent lord of the rings mods (sorry i forget the name), this puts the game in the hands of players who would not normally touch it and they may buy future releases if they get into it. I know that i will buy kingdoms again when the Europa Barbarorum II mod is released (I lost the game dvd when i moved house last year). If it werent for that mod coming out i would not repurchase the game.