At least in that case they were a year apart from each other (iPhone 3G 2008, 3GS 2009, iPhone 4 2010) on the normal release cycle.
I thought the furor over the 3GS was from people who bought the original 2007 iPhone at the non-subsidized price and then turned around and traded up to the 3G model at launch and paid the subsidized price. When the 3GS came out those folks were halfway into two-year contracts and didn't have any upgrade options with AT&T, so they couldn't do the same again, and felt slighted that a year later a better phone would come out and they couldn't get the subsidized price.
And that's not Apple's fault, that's just nerd rage over what happens when you buy a carrier-subsidized cell phone.
I thought the furor over the 3GS was from people who bought the original 2007 iPhone at the non-subsidized price and then turned around and traded up to the 3G model at launch and paid the subsidized price. When the 3GS came out those folks were halfway into two-year contracts and didn't have any upgrade options with AT&T, so they couldn't do the same again, and felt slighted that a year later a better phone would come out and they couldn't get the subsidized price.
And that's not Apple's fault, that's just nerd rage over what happens when you buy a carrier-subsidized cell phone.