Actually, I didn't mention the 4.8" screen and wasn't specifically referring to that one. All of the Android screens are in the 4+" range, I think most around 4.3-4.5, even at the low end of the price range. But of course there are a lot of phones which have a wide range of screen sizes and types, and the S3 is at the top end.
Apple does have a free phone (3GS) and a competitive cheap one (the 4 starts at $99), so if price was the main consideration we would see those sales going to Apple if all else was considered equal. The fact that Android is still gaining implies that other features, such as the screen among others, are compelling enough to sell the phone.
I figured the free 3GS would be brought up. The flaw in that argument is that it is only available on AT&T and the available rate plans on AT&T are still much higher than most people are willing to pay. Those low end free Samsung phones are available on EVERY carrier including the budget ones like Cricket, Virgin, Boost, Metro PCS, etc. Someone who just wants a smartphone can walk into Cricket and get one for free and only pay like $45 per month for service. Observe the customers that come into any cell carrier store for a day and the first thing most people ask is "what kind of free phones do you have?" For every carrier other than AT&T, it's usually an Android device. Now if Apple decided to throw the free 3GS to the low end carriers to compete with Android, then this would be a fair comparison. Won't happen though because their rate plans are too low for Apple.
I think people see those marketshare percentages and forget that there are tons of carriers other than AT&T/Verizon and Sprint that are for the most part Android only(Yes Cricket and Virgin have the iPhone now but it's damn near full price to get it, not free or even $99). T-Mobile alone has like 33 million customers and they're offerings are 90% Android.