That's how apple can milk the iPhone loyalist..... Only come out with a 4.2" screen for the next phone. Then the S version, ( with minimal upgrades), then the next version can go up to 4.4", then two versions of that, and so on, until they get to 4.7 or 4.9".
Just think... Apple could have phone the size of the S3 and the HTCs in about 8 or 10 years! Think of the milking they could do (and its not too far fetched).