Yes, there's quite a bit of difference between an iPhone 6 and an iPhone 5s. I think that we as consumers are very superficial, so we only look at the cosmetic changes. Under the hood, the iPhone 6 has a more powerful processor, a better screen, a better camera, and all sorts of other upgrades from the 5s.
In the real world you only get big changes for the first to or three installments. Sometimes not even that. Then it's just same old, same old until they can't get away with it anymore. Then they make one or two more big updates and then right back to the same things.
The iPhone 6 is not really that much different from the iPhone 5s. in fact, Apple has not made any real big improvements on each "upgrade" to the iPhone. They just do it in smaller increments so they can exploit and bleed their customers dry at every single possible turn.
When is comes to a good marketing scheme, especially when it's something like an iPhone, you don't want the next thing in the line that you put out is "the best you can do". That way you can make another one, and sell it for more. Just little tweaks here and there to improve it, and once everyone has that one, you make one that's just a little bit better, and etc.
An iPhone 5s and 6 are similar. There should not be so much hoopla surrounding the new unveiling. It is essentially the same product just worked over to be slightly more efficient. It does make sense to sit outside all night just to buy the updated version when the store first opens. It isn't that big of a deal.