That's a ridiculous thing to say, sorry. The 4S may have looked like a 4 but it was all new inside - much better camera, dual core processor for the first time, completely re-engineered antenna (probably the first iPhone that was genuinely good as an actual phone), it's actually still a great phone and runs IOS 7 like a champ.
Weakest update? Probably the 3G in hindsight although it didn't really matter at the time. It really was just the original iPhone, with a plastic back and a 3G radio - everything else was the same, same awful camera, same processor (that quickly showed its age when IOS 4 was released) same everything.
The reason it didn't matter was because (a) it was much more widely available, and cheaper than the first so for most people it was their first iPhone, and (b) it came with IOS 2 and the very first App Store pre installed so quickly started doing things that the original hadn't been capable of (until the update).