The S is for speed and for more speed one needs some more power. T-Mobile Netherlands has posted specifications for the new iPhone 3G S processor revealing a 600 MHz chip inside.
The new chip and more ram is how the iPhone 3G S is 50% faster than the iPhone 3G. For the iPhone 3G S Apple has bumped up processor speed from 400 MHz to 600 MHz and doubled the RAM going from 128 MB to 256 MB.
While no more details about the processor in the iPhone 3G S have emerged yet we are expecting it to be some sort of ARM 7 processor previously rumored.
Also, Apple's "iPhone How To" area has an entry on cleaning the iPhone which mentions the new iPhone 3GS will have an Oleophobic screen. You were hoping for perhaps OLED? Well how about an anti-climactic anti-oil screen?
To clean iPhone, unplug all cables and turn off iPhone (press and hold the Sleep/ Wake button, then slide the onscreen slider). Then use a soft, slightly damp, lint-free cloth. Avoid getting moisture in openings. Don’t use window cleaners, household cleaners, aerosol sprays, solvents, alcohol, ammonia, or abrasives to clean iPhone. If your iPhone has an oleophobic coating on the screen (iPhone 3G S only), simply wipe your iPhone’s screen with a soft, lint-free cloth to remove oil left by your hands and face.
Apple via iClarified