So we're getting one next week - but why not sooner? That was one of the takeaways from this article. Pace of innovation has slowed under Tim Cook.
The only difference this year is that Intel has been having problems delivering on time (and without problems).
That is the entire difference. You're correct in that this is the expected time between redesigns, but we also haven't gotten a spec bump in over a year. That's unusual, and it's giving real fuel to the usually-overblown "[product] is so stale!"
The only thing that Apple could have done is bump the CPU, which would have not gained anything in terms of power savings or any other changes, and means now you have one more model you have to stock replacement parts for.
This has been an issue not just for laptops, but also for their Xeon line-up in servers. Due to manufacturing delays the v4 for the Xeon line-up was released earlier this year, and didn't really get started shipping until April.