Folks seem to forget that not everyone has the option of switching carriers. The most obvious example of this are people who get their phone from their company via a bulk contract with a particular provider, as I used to when working at a large bank. If your company is only offering you Verizon service, you're not going to give up an essentially free wireless account on that carrier to pay $100/mo for an ATT account, even if you would rather have an iPhone. A lot of folks are also not aware of number portability yet - I still see notices that folks have changed their numbers because they got a new carrier - so they may think that buying an iPhone on ATT would mean changing numbers.
Do you mind sharing your age range? The reason I ask is, I work for an agency, and we have blackberry service provided by T-Mobile, which we are free to use as our personal phone.
However, most people, especially those 35 and under, and our technically inclined folks, all still carry their own phone. Primarily because they want the iPhone, or in some cases, want Android.
It's also worth noting that overseas, where the iPhone is not tied to ATT, Apple continues to outpace Android significantly: http://www.clickz.com/clickz/stats/1733041/apple-google-cont...