Maybe it's by design - if something is consistent across all pages, you're less likely to notice it, and less likely to click on it. Error boxes have consistent interfaces - "OK" and "Cancel" - and even when they're important, most of us just click OK. By changing it up, by making it different, they're making you look at it.
For ProApps (Logic, Final Cut, Shake, et. al.) the marketing sites are black and silver. The buttons reflect that clearly. Also, the buttons will use the arrow icon.
For iApps (iTunes, iLife, iMac, et. al.) the marketing sites are lighter in color typically now in blue or grey. The buttons, again, reflect that and the use a triangle icon.
That said, each product has its own design team (which is why the buttons vary slightly) but everyone reports to a creative director (Apple Support works differently) which then reports to a marketing director so that Apple style guide is observed and the design is consistent. The iApps sites have to have explicit Jobs approval before publishing.
The International web team dynamic is also interesting. Prior to publishing, they're flown in from all over the world, put into a meeting room on campus for an entire week prior to some big event. During that time all the sites have to be localized, translated, updated, and approved in tandem to the US launch.
This is true also for their desktop apps user interface. This trend started with Mac OS 9, when QuickTime started to use that stupid brushed metal theme. Currently there few themes in Apple apps; Aqua (Mail), brushed metal (Safari), iApps (iTunes) and pro (Final Cut).
This make it tricky for 3rd party apps - you have to ask yourself which group your app belongs to. If you want to create iApp or Pro interface, you have to simulate the design because there are no ready made interface elements using those styles.
What's going to be REALLY inconsistent is when Leopard comes out. No one has a clue as to how to deal with it on the continuity because Steve wants it to be black and silver, to match the iMac.
