- You don't wait 16 months for just a speed bump.
- You don't let your iconic ceo step down and have you're replacement, which everyone in the tech industry will be harshly judging, launch your next, and most anticipated product being only a speed bump.
1) Perhaps the Assistant software wasn't ready, or perhaps they didn't want it so close to the Verizon release. Also, LTE isn't ready for prime time yet (5 cities in the US, a handful in Canada, Sweden, and Korea don't justify a global release just yet), so a 4S with a more substantial "iPhone 5" next summer might fit nicely into Apple's plans.
2) It isn't as if we know how Jobs' resignation was timed. It's entirely possible he thought he'd still be CEO and would step down later or even recover and come back full time.
I would like a more substantial iPhone 5 release tomorrow, and up until this weekend's developments thought it was a good possibility. It still might, but it isn't as if the 4S would be a mere speed bump. The software update for the 4S appears to be very substantial.