Price drop could also signal that they've cut the cost of making them? I know it goes against the reasoning that lower costs equals a higher margin, but maybe Apple is setting up for a Retina only MBP lineup? While Retina Airs sound amazing, I still think they require a bit more oomph then they have.
Also, take a look at the pricing scheme of the current lineup without the 13" Non-retina MBP:
Macbook Air: 11" $999/$1099
Macbook Air: 13" $1199/$1399
Macbook Pro: R13" $1499/$1699
Macbook Pro: 15" $1799
Macbook Pro: R15 $2199/$2799
I see the 13" Non-Retina Macbook Pro going away soon. It doesn't "fit". If they can bring the pricing on the 15" RMBP to $1999/$2499 (a similar drop to what the 13" RMBP saw), Then maybe you could make the argument that the 15" MBP could go away as well. Retina displays on the MBP, regular displays (and longer battery life) on the MBA.
Just a thought.
If I were to guess, that's precisely what I think it's going to happen in the next refresh. It makes perfect sense for Apple to get rid of the non-retina models, so the line of laptops would look like as follows:
11-inch MacBook Air: US$ 999/US$ 1,099
13-inch MacBook Air: US$ 1,199/US$ 1,399
13-inch MacBook Pro (retina): US$ 1,499/US$ 1,699
15-inch MacBook Pro (retina): US$ 1,999/US$ 2,499
With a price premium of US$ 500 over the higher-end 13-inch MacBook Pro with a retina display, it is the 15-inch model that seems a little bit overpriced now...
Apple might even re-introduce the 17-inch MacBook Pro, for some US$ 2,799, now with a retina display, as future video cards will allow for a resolution even higher than 2880x1800.