Because if it does follow the tradition as you say, I think Apple will be in a bad position. Another year of a 3.5" display?! I agree that the 4.3" androids are excessive but a 3.7 or 4" on the next iPhone is a must.
the 3.7" and 4" on the Incredible & Incredible 2 respectively , are the perfect size screens IMHO. However, i don't want the iphone getting any wider, longer, or thicker. If they filled up the borders and made the screen bigger like the incredible 2 than i would be fine/happy with a 3.7 or 4". However, 3.5" is perfectly fine too.