Dean Bubley has a nice thought provoking piece about branded mobile handsets vs. the plain vanilla versions. In the USA it really doesn't matter as few people really need the unlocked versions since AT&T and T-Mobile are the GSM players and if you're a happy domestic customer going global with an unlocked phone simply means buying on on eBay or from an etailer who sells them.
But for the UK and EU residents this is a big deal. Crossing borders, swapping SIMs or using a travel SIM like MaxRoam or SIM4Travel (now owned by client Truphone) is a big deal.
What we're beginning to see is carrier clout being applied in both directions (retailer and handset manufacturer) to keep more of the business on the carrier's network as long as possible. This approach will reign as long as the governments permit a closed market over the public and licensed airwaves.