I think that's the reason for the delay right there: they're holding back the new models until Mavericks is ready (just like the mid-2011 Mac minis and MBA were held back for Lion).
The benchmarks we've seen for the new rMBPs have all had a custom build of Mavericks. Further, it does not make sense to develop a whole new build of Mountain Lion in tandem with a custom build of Mavericks.
As such, you won't see Haswell MBPs until Mavericks is available for sale.
This line of reasoning makes absolutely no sense.
• You said, "the benchmarks we've seen...have
all," but there's been one benchmark that popped up.
One. I do not understand how people are contorting that single anecdotal data point into thinking that there can't be a ML build.
• Moreover, we are not talking about official or even sanctioned tests. This is an "oops" event by a person at Apple who should have known better but screwed up by running Geekbench. Why would you think that just because one guy is running a dev build on his laptop that there aren't other configurations/builds/etc. in use?
• 10.8.5 is in beta testing right now. It wouldn't be entirely trivial to be sure it's adapted for new models, but it's also not a massive undertaking. And, keep in mind--that's exactly what Apple did last year with the release of the rMBP. And that was even
during a time when supply was seriously constrained.
• Holding back the models for an OS release is just, well, insane from a business perspective. This is a company that is struggling mightily to avoid year-over-year declines in revenue. While supply chain issues are involuntary and cannot be helped, there simply aren't many good reasons to
voluntarily delay your flagship, sales-leading product.