Simple, for power users at least these that travel abroad (and most do at least for a couple of weeks per year), the first thing is how easy it's to change SIMs.
In most (at least European) countries you can get something at least vaguely acceptable (especially for data access) as a prepaid SIM. Data roaming on the other hand is practically never acceptable for usage on smartphone.
For this let's compare the iPhone with the HTC Dream/T-Mobile G1.
First difference, the T-Mobile G1 is available as HTC Dream without lock. OTOH, most people in both cases will probably have gotten the simlocked version.
1.) unlocking experience on the iPhone: 2 days wasted trying to get a jail break going. 3rd day included a visit to a seedy 3rd party phone shop that advertised jailbreaking iPhones. Always in danger of undoing it all via iTunes that persistently tries to offer an upgrade for the phone.
2.) checked that the G1 is really simlocked, bought a 20 unlock code online, used it with my SIM of choice the same afternoon in the office.
Actually, both events happened some months ago, but I cannot remember the details of item 2 (as if the G1 was really locked), while item 1 makes me shudder. (Actually it's as bad that the iPhone got a non-smartphone assigned to cover wheneever the iPhone decides to go dead). OTOH, the G1 unlock did happen when the phone was very recent on the market, while the iPhone 3G jailbreak happened when the 3GS has been longer on the market than the G1 mentioned. And I'm still unclear how jailbreakable the 3GS are.
Next important item on a frequent travelers (that's what I admit is not exactly critical to the majority, but it's an important item about who controls the device that I own) is sharing Internet access. Obviously, a smartphone cannot manage to fill completely an UMTS uplink, so there is no drawback in sharing it's connectivity.
1.) the iPhone started to work as a tether after some months, basically after a couple of upgrades and the jailbreak. It offers USB Windows-only (perhaps Mac too?) tethering and standard PAN Bluetooth networking.
2.) the G1 offers TCP forwarding tethering via USB and after rooting, it offers a standard NAT-ing Linux kernel based router via Bluetooth or WLAN. The USB based tethering I was capable to use easily enough on day 1 to establish a full VPN (albeit TCP based) connection from my laptop. In practice the standard PAN Bluetooth networking is nicest for me personally, but everyone has probably his own favorite.
So I do not think that the iPhone rules the "total experience dept", as it's a total fail on two important items (one of general interest, even if they do not know, but they will when they go on their next holiday), so it's not even in the running for a phone here. (Ah, I learned yesterday why my wife got the iPhone 3G last year, "it was the cheapest colorful toy for our daughter that we could get back then easily and quickly", and "yeah that Motorola Droid looks cool")