You need to remember that a goodly portion of the boot process occurs BEFORE Windoz, or any other OS, starts to load.
& that may be where most of the problem lies.
I haven't personally researched it, but Maximum PC mag had an article that stated the BIOS was the main culprit for slow boot times.
I'm not sure I buy it, because as 1 post put it, there does seem to be some level of conspiracy to keep as steep as possible of an upgrade path going.
That really doesn't excuse Windoz (or others) of not designing a post and load sequence that would assign & execute boot priorities in a safe & reasonable order.
I guess its more profitable to ignore the way to speed boot times than to actually try to resolve such issues.