The iPhone 4S has been criticised by some for being little more than a speed bump. Device sales have been incredibly strong
—buyers clearly aren't concerned about this issue—but evidence also suggests that there've been more changes than are externally visible. The phone's dual-band antenna and updated camera are both different, while the CPU is reportedly based on the Cortex A-9 as opposed to the A4's Cortex-A8 heritage.
This last would help explain why preliminary performance tests indicate that the iPhone 4S dominates every other phone and tablet save for the iPad 2. Moving to a dual-core accounts for some of the boost; the Cortex-A9 architecture delivers the rest. The 4S also uses DDR2 instead of DDR, a different baseband processor. The Qualcomm MDM6610 is what guarantees the phone's compatibility with Sprint, AT&T, and Verizon.
The 4S keeps the same 512MB of RAM as the iPhone 4, which iSuppli believes is a testament to the memory efficiency of iOS. Certainly there's little evidence to suggest that iOS devices are memory starved; the iPhad family outperforms tablets and smartphones with double its RAM.
The huge number of pre-orders and activations suggests that analysts who decried the phone as a disappointing update were giving voice to their own frustration at having mistakenly predicted the iPhone 5 rather than actually voicing public sentiment. Siri, iOS 5, and the performance boosts the new phone offers are apparently more than enough reason to spur consumers to update—even if the talking heads weren't particularly impressed.