I'd also love to see iPhone 4/4S vs. SGS2/3 (and Note) head-to-head numbers and I tend to agree with OGroteKoning... An "entry" level iPhone, not a two or three year old 3GS, would be trouble for a lot of the other manufacturers.
The thing about the 2-3 year old 3GS is that on specs, most $99 phones of the last year were pretty evenly matched with it. What was high end filters down to medium and low end eventually. Versus the Galaxy Ace for instance it's a washout. And it's had 2-3 years in which to build up fantastic app support, which a new design can't boast.
Not to mention the savings in R&D and engineering that they can leverage.
Put it this way; if Samsung released the SGS1 now on a R149 contract (or whatever the equivalent), do you think it would be popular? I reckon definitely. It's still a stunning phone.