So, er, let me get this straight...
... they asked people how many dropped calls they were getting, but didn't bother to look at the *context* of those dropped calls?
Even the London Underground has no cellphone reception in the underground sections yet; it's expensive to fit this sort of thing. I don't know how many US cities have wired-up their road, pedestrian, subway tunnels and other infrastructure which would otherwise have no cellphone signals *at all*, but I've not seen any data suggesting it's much better over there than it is here in Europe. Dropped calls are *normal*. And 4.8% is hardly anything to get too excited about. That still means 95.2% of calls are NOT getting dropped.
Considering the sheer size of the United States of America, and its tiny overall population density, that's actually pretty good. I've lived in parts of *London* that *still* get terrible GSM reception today.
If I'm using a mobile phone via an in-car hands-free kit, I'd *expect* a call to be dropped if I entered a tunnel. GSM is rather less common in the US, and tends to be much more concentrated around urban and suburban areas according to the coverage maps. The CDMA networks have had longer to spread out and are more common generally even in outlying rural districts. That's inevitably going to skew the data in a survey such as this. (And let's ignore the fact that CDMA iPhones have only been in the wild for two months or so, not the three covered by the survey.)
As cellphone networks spread and improve, the call-drop rate should fall, but is unlikely ever to reach zero, regardless of whether you're using CDMA, GSM or bloody Iridium.
Judging by the complaints on various websites—which is no less "scientific" than the survey reported on by this article given that both have strong self-selection biases—the problems with AT&T's network aren't caused by the iPhone. They're caused by AT&T's network coverage. For every whinge about dropped calls on an iPhone, you'll find another claiming they get *better* reception with their iPhone than they did with their old, non-Apple, phone. (That's certainly been my experience: I wouldn't go back to a Sony Ericsson or Nokia if you *paid* me.)