I am not sure I agree with that -- I think it's a generalization made by people with limited experience.
I am the one responsible for device/carrier testing at my company, and here's my fleet last time I photographed it in September (photo taken with another iPhone, so it's not shown alongside the three others):
Click to view quoted image
I will tell you right now that the differences I see have more to do with carrier and signal strength than the phone or device. In this area, BB and iPhones on AT&T have much poorer coverage. I don't track dropped calls, since we'd be talking 2-3 drops per 100 calls. But what I do notice is that there is poor or no coverage in parts of the area with AT&T. This causes all the devices to have issues on AT&T -- poor quality, can't make calls, or don't receive calls. It doesn't matter if it's an iPhone or a BB.
It's a totally different story on Sprint and Verizon. All the devices are solid, and that includes the iPhone 4 and 4S. I switched to Verizon for my personal 4S, and it's a night and day difference with AT&T. I can totally see why the iPhone had such a lousy reputation for call performance when it was chained to AT&T.
In different parts of the country, it's a different story. If I head up to a nearby major city 40 miles away, AT&T is solid (and so is Sprint/Verizon of course). As far as I am concerned, it's all about the network, and the device is secondary. I wouldn't see such a big difference between AT&T and Verizon, with equivalent iPhone 4 and 4S devices, if the problem was with the device.
But, hey, that's just me, with the actual experience and expertise. You can always believe HeShootsAndMisses who needs to come up with kiddy names to make a point. God forbid there should be legitimate experience/knowledge involved.