But the SSD, soldered RAM, display and battery differences exist in the 15" cMBP to rMBP comparison, too. Actually, the marginal cost of going retina, along with increased battery to drive the pixels, are *less* with the 13"
Yes only if you look at it in a non-normalized perspective. It is actually a larger percentage increase increase for the13" than the 15". In general, more expensive products can "soak up" a higher priced component change more easily. For example:
$600 other stuff + $100 screen for 13" ( $700 )
$750 other stuff + $120 screen for 15" ( $870 )
say retina adds another $90 in cost to both screens. The 15" sees a 10% bump and the 13" sees a 12% bump. Even if the retina scree was a $102 jump the still smaller, 11%, than for the 13".
It is a smaller increase dollar wise but it will have a bigger impact on demand. I don't think Apple is positioning this to be a relatively (to the other 13") high volume seller in the first year or so of being on the market. If it has no dGPU then it will have weakness that will likely require the next Haswell update (meaning next year) to resolve more satisfactory for those more focused on 3D graphics performance.
Maybe. But notice that the retina MBP ($2200) starts at *the same* as the top of the cMBP offerings. ($2200).
Apple needs another 13" laptop priced at $1499 like they need a another "hole in the head". They have already got 2. Three would be in extreme conflict with Apple price approaches of the last decade.
Apple's 15" prices are relatively high to even competitive quality 15" offerings. Remember, the 17" died at the $2400 price point. There is significant enough overall market pressure not to stray too far over the $2000 boundary.
It goes back to the huge difference between the end of a pricing range and the middle. The dynamics are not the same. There is downward price pressure in the middle of Apple's laptop range to from the market but it hasn't killed off any mac models in the middle yet.
We'll see, if the 13 rMBP is really $1699, I think it will have a quad-core (and possibly dGPU) differentiating it from the similarly spec'd 13" MBP. But I could be wrong.
If the recently leaked pictures are correct and Apple went to "thin as possible" then you are quite likely wrong. Soldering the RAM to the motherboard will largely nuke any space savings that removing the ODD would provide. There wasn't room for a dGPU before and there won't be one now if use the ODD space for things had before (RAM and batteries now soaking up more horizontal space because case height shrank). ( dGPU have an addition RAM soldered to the motherboard issue in addition to the GPU package itself and associated thermal problems. . Either that or they have crippled the machine by soldering just 4 and 8GB to the motherboard. So would have a dGPU but the memory is kneecapped.
The value proposition is going to be "very close to MBA weight". If there is less than a 0.8lbs difference between rMBP and MBA they will likely paint it into the same class.
Likewise the 'classic' MBP 13" don't have quads (and i7 class ). If it got the machine a significantly faster HD4000 implementation perhaps, but it doesn't.
As I alluded to before there is a big difference if measuring this rMBP 13" relative to the MBP 13" or MBA 13". Relative to the MBA 13," a 'regular' i5 is a step up and so is HD4000 at non dramatically underclocked speeds.
It isn't necessarily former/current MBP 13" buyers they are looking to be the primary block of the customers for this initial version.
Oh yeah call it "Retina" if you like it, but this is just a marketing term. 
