If you really look at both types they are really quite the same in regards to the cardiovascular system. It is more difficult to get your heart rate and keep it at a certain rate for a long period with weights, but it can be done. But you dont want to be doing this anyways. Cardio is more effective when you do interval training. Weight training is simply cardio with a lot of resistance and little rests. WHIle cardio is a lot less resistance with no rests. Both work your heart very well.
I've probably done cardio 5x this year and my resting heart rate is 60bpm. Now this isn't amazing but if you take into account I weighed 255lbs when I took this my heart is working harder than it would have to if I was 160lbs like I was when I started lifting. So I think that is a good gauge of how healthy my heart is.
I think weight training gets a bad rap because people only do the fun stuff. they do biceps and chest, they never stretch, they stay away from lifts that include large muscle groups, and most of all they are lazy. They do a set of bench press then lie to their friends about how much they did last week. YOu gotta keep the pace up to work your heart.
If you lifted hard, watched what you ate, stretched, did lifts like, lunges, dead lifts, etc I really see no need for cardio, as your heart and auxillary muscles are getting worked plenty hard.
BUT!!! some people like cardio you do get a good feeling from it and you dont get as sore. So if you want to work the heart without moaning the next morning from being sore then do cardio.