I have a hard time gaining muscle so when that is my goal, I do not do cardio. The NSCA states that endurance training has a negative effect on strength training (but not vice versa). I agree with you other ladies, but I have a hard enough time getting all of my kcals in, and I don't want to have to eat even more because I voluntarily expended more. Also, to continue getting the benefits of cardio, you have to increase either the time or intensity progressively, as your body will adapt to it very quickly. Before you know it, you would be back to 5 days a week at 45+ minutes.
It is not the same as doing cardio, but you heart will adapt just fine to resistance training, especially if you keep your rest between sets short and pick up the pace during your lifting session. and as a gym athlete, I'm sure you are more active in your daily life (brisk walking to work, taking stairs, etc.) that you are keeping your heart healthy. Personally, I have found it more beneficial to my gaining goals to not incorporate cardio.