While I can only speak for me, my two brothers, and father, I assume they're are others like us. I first played medieval total war and viking invasion and fell in love with total war. This was the greatest game I had ever played. I was learning history while I played an amazing strategic game. I than told my family about it and we all got Rome with excitement. It was a good game [ I got to learn history here as well] but it was missing something from medieval and I was not sure what. I later concluded it was the battles that have been super charged for speed and a loss of immersion in the game. In medieval I felt like I was a king in the time period. However my brother found an amazing mod called Rome total Realism and that made Rome a great buy.
I than bought medieval 2. This had improved over Rome in areas such as the battle speeds, but the AI and lack of MP campaign [along with all battles being sieges] kept it from being a great game and diminished my excitement for total war games. Empire was a vast improvement and added the much needed campaign mp but in a unreliable beta version. However I was back in love with total war ready to buy all the new titles.
Than came shogun, I did not buy it as it was a time period of no interest to me. But given total realism type mods, I would buy it later if a mod came I liked. However this never came and the battles were back to super speed and worst yet, RPS combat controlled victory from what I was told. I was done with total war.
But not for long. Rome 2 came out and was advertised as fixing many of the things I disliked about shogun. Less RPS effect, slower battles, [jack lusted you sneaky liar] and more historical authenticity. I thought for sure total realism would be able to fix any remaining issues so I bought the game assuming total realism could fix it. However this game was the worst yet, they had not only not fixed the issues, they added magic buttons in battles so the winner was who could click the right magic button the fastest and who could match up what unit with their counter unit [RPS] gone were the epic strategic, battles of medieval 1 and viking invasion. Terran, morale, holding your line, flanking etc matters less than hitting a magic button. Decision's on the campaign map seemed to have no actual effect on how well you played. But worst of all the game could not be fixed through modding. I had never been so disappointed [my fault for getting hyped up] in a game, it was the Indiana Jones 4 of video games.
I have not since bought a total war game. However my interest was peeked when I heard of warhammer total war. If CA entered fantasy maybe my beloved lord of the rings might happen and it would fit perfectly into total war and the game makers could still have their magic buttons, but it would be ok. Or better yet, maybe a mod of LOTR for warhammer would be created. Sadly it was found out this game was not modabel so I did not buy the game.
Ok I have given the backstory. I will not buy another total war given the direction they have gone since shogun 2 is not to my liking. Its sad but even a LOTR would likely be butchered. Clearly the sales are good but the direction is not for everyone.
How it effects sales
Lack of modding effects sales a few ways. I dont buy any games unless they can be drastically improved through total conversion mods. If a medieval 3 came out and could be modded the way medieval 2 games could, than without question I would buy it. Just see what the third age mod did. I bought kingdoms expansion years after third age was finished just to play the mod. If games could be modded like that than I would be willing to buy vanilla at release such as I did with Rome 2 with the anticipation of mods improving the game. Instead the games end with a no sale because of lack of modding.
So when CA looks to number of sales after mods are released to view the impact, I think they are missing the majority of would be sales that modding could provide. They just dont see those numbers because those are people not buying the game at all, like me. I dont see a reason why I would not buy almost every total war game if it had the ability to be a total conversion mod similar to the way medieval 2 total war was.