Let's define what "cardiovascular exercise" is (or alternatively is not):
The crux of the issue is that you don't need to be strong to perform cardio. Even someone like Lance Armstrong isn't really strong. Lance doesn't have strength but he does have a unique ability to perform very hard work over long periods of time.
When cardio is performed, strength demands are not high as is the case with weights. In cardio, muscles are working hard but not under major duress. So they shouldn't experience much in the way of lactic acid build up if you're an athlete.
In the case of absolute elite athletes such as Lance, someone once worked out that Lance can sustain the equivalent of 145 pound squats for maybe 20 minutes at speed (which corresponds to a sprint attack on an Alp). So, at the elite end of the spectrum, the most weight an athlete will endure is about 140 pounds. Well, we can all of us squat that.
Where bodybuilders and strength athletes experience difficulty is over this lower key kind of performance where strength isn't an issue but sustainability is. We don't train to endure lighter and continual stresses after all.
I mean, even in circuit training we'll be lifting more than the said 140 pounds.
In a nutshell, to directly develop heart and lung, blood and oxygenation capacity, we need lighter loads than in the gym and the heart rate constantly high enough to make talking difficult while training. We need to be dripping sweat and enduring such a situation over, say, 50 minutes minimum.
As someone else said above, it does make sense to test yourself. Take a pulse reading at rest and then perform either a 30 minute, hard cross-country run or maybe a 40 minute MTB ride. Note your pulse throughout the cardio session and compare it with an iron session in the gym.
Personally, I find my pulse does get very high at times in the gym during deads but, of course, it goes down again when I bench press or rest between sets.
I could keep it higher by supersetting bench with squats but the drawback is the load would still be too intense for optimum cardio and a bit too light to build maximum muscle.
It is, IMO, quite possible that a trainee could get both strength and CV work from a well thought out program. The rub is it would not be fun, and it would not be easy. The majority of the exercises would have to be compound exercises with a focus on the hips, thighs and lowerback.
Upperbody supersets just don't tax the CV system as well.
