Actually, I see OS X Mountain Lion not as a service pack, but rather part of a tick-tock cycle; much like how Intel does processor releases (and Apple has handled new iPhones since the 3GS). I don't think Apple's trying to synchronize OS releases with Intel CPUs, but rather is adopting Intel's tick tock model as their own.
As for the change from Late Summer to Summer for Mountain Lion's release, this suggests that Apple's finally gotten over their headaches developing Leopard / Snow Leopard and new iPhones at the same time. In fact, I'd even go so far as to say their development process is now a well-oiled machine; slick enough to coordinate releases of both once per year on a regular basis without slipping. Apple couldn't have achieved this feat without both some internal reorganization of their development teams and leadership from Tim Cook, IMO.
What I suspect Apple is doing internally with their development teams is this: There are now a total of 8 development teams, each with a well-defined role. 4 of the teams work on OS X; the other 4 on iOS. The 4 OS X teams are divided as follows:
- Team 1 works on The Next Big OS X Release (Mountain Lion)
- Team 2 works on maintenance of the current OS X release (Lion)
- Team 3 works on security fixes for the previous OS X release (Snow Leopard)
- Team 4 works on planning for The Release After The Next Big One (name unknown, and will almost always be unknown)
The 4 iOS teams are divided as follows:
- Team 5 works on The Next Big iOS Release (6)
- Team 6 works on maintenance of the current iOS release (5.1)
- Team 7 works on planning feature updates for The Next Big iOS Release (6.1, 6.2, etc.)
- Team 8 works on planning for The Release After The Next Big One (7)
When release time comes around, each team rotates into a new number. 1 -> 2, 2 -> 3, 3 -> 4, 4 -> 1 for the OS X teams. As for the iOS teams, 5 -> 7, 7 -> 8, 8 -> 6, and 6 -> 5.