The fact that the iMac doesn't have Thunderbolt 2 doesn't really signify to me that the Retina MacBook Pro won't recieve Thunderbolt 2.
Lets just take a step back and look to WWDC in June. They released updated MacBook Air's with everything the new iMac received. Haswell CPU, 802.11ac networking, PCIe based SSD Stick.
So if they have the same upgrades why didn't the iMac release back in June? Because the CPU that the iMac uses wasn't ready. Similarly the Retina MacBook Pro did not debut at WWDC ether.
So lets fast forward to this month the new iMac releases and yet still no new Retina MacBook Pro. Based on what you're saying the Retina MacBook Pro will have the same upgrades that the MacBook Air and iMac received, Haswell CPU, 802.11ac networking and a PCIe based SSD Stick. So why isn't it released?
I would surmise the same reason the iMac wasn't released at WWDC. There is a processor holding the MacBook Pro's back from being released and I believe that to be Thunderbolt 2 which we all know is coming before the end of this year in the Mac Pro which again isn't released yet.
This to me is significant because they showed the Mac Pro off at WWDC on stage in post-keynote sessions. And by this I mean they actually had one being used by presenters as developers were there. This indicates the hardware was finished to such a degree they felt confident enough to use it in-front of hundreds of people.
So why isn't the Mac Pro released yet if it was already finished in June? Because of Thunderbolt 2. It was obviously using sample silicon from Intel and we know that Thunderbolt 2 isn't coming to the end of this year.
So to me this all points to rMBP and Mac Pro releasing at the same time in the future with Thunderbolt 2.
As to why the iMac never received Thunderbolt 2 I would argue it's a consumer machine just as the MacBook Air is, if it has Pro in the name (Mac Pro, MacBook Pro) then it'll receive Thunderbolt 2 this year and then next year we'll see the consumer products receive Thunderbolt 2.