@Bleezy, I don't think the 1st installment will be affected sales wise, with the addition of the 2nd and 3rd game releases. The only way that would happen is if a) the 2nd and/or 3rd release very quickly after the 1st (some people may just want online or don't care for 3 campaigns) or b) the 2nd and 3rd releases can stand on their own storywise (not have to play the 1st SC2 Terran game to understand). I think a) is quite possible but b) is unlikely, but a) won't have a huge impact on sales of the 1st game. Sorry if that was convoluted.
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I don't think the 1st installment will be affected sales wise, with the addition of the 2nd and 3rd game releases. The only way that would happen is if a) the 2nd and/or 3rd release very quickly after the 1st (some people may just want online or don't care for 3 campaigns) or b) the 2nd and 3rd releases can stand on their own storywise (not have to play the 1st SC2 Terran game to understand). I think a) is quite possible but b) is unlikely, but a) won't have a huge impact on sales of the 1st game. Sorry if that was convoluted.