I think with the 5C, 5S, and iOS7 they've just been too sidetracked to make macs a priority. After all, Macs are just a tiny portion of Apple's revenue and fiscally speaking, one can't argue with that logic if it's true.
Sadly I've felt this to be the case since the first release of FCPX, and you can't blame a company to capitalise on profits... Expect Glencore.
I really thought we would have at least seen an update by now or an announcement for when the new rMBP would be available.