Lies, damned lies and statistics 🙂
Part of it is a chicken and egg situation. Designers create sites that work well on iPhones (and only iPhones) and are surprised when no one else visits them.
Advertisers target these sites and report back that only iPhones use the mobile web.
Tomi Ahonen has an excellent rebuttal of these “statistics”.
The other issue is that the iPhone is commonly sold with an “unlimited” data plan – so the users use it more. But that doesn’t make for more users. If an iPhone user looks at 1,000 pages a month, is she more worthy than 10 N95 users who only visit 100 pages a month?
Finally, even if what you say is true, developing an app is harder and more expensive than building a website. And it relies on the user installing something to their phone(s).
Build a website; it costs less and targets everyone.