Microsoft now seems to understand the advantage of a tighter ecosystem, as Windows 8 attests. Windows 8 adds the equivalents of iCloud and Time Machine, for example. But there's no native equivalent to AirPlay or AirPrint. For streaming, Microsoft could impose a standard on DLNA streaming, which is deployed in a highly fractured way in many consumer electronics and Android devices. Until it does, companies like HP and Dell are stuck. They can go all-proprietary, as Samsung has tried in the Android environment to poor effect -- or just wait.
Similarly, look at how Apple has approached the slow integration of OS X and iOS, bringing increasing touch capabilities to OS X, while providing simple hardware (the Magic Mouse and Magic Trackpad) to retrofit almost any Mac for touch. In the PC world, Windows itself has limited touch capabilities that don't work well, and you need to buy a new PC to get touch capabilities. That's a sure way to create a confusing, fractured ecosystem. The supposedly touch-savvy Windows 8 shows that in spades.
I don't mean to suggest for a moment that Apple is perfect; its handling of the iPhone 5's new screen dimensions and Lightning connector port shows it too can neglect its ecosystem. But because Apple runs the whole show, it can design the whole experience. By contrast, the Windows universe is a federation of hardware, operating system, application, and service providers that will always have some stitched-together qualities. In that world, the company that pits the guts in a case and installs someone else's OS and apps can only play with the surface attributes.
The real problem that HP and other PC makers face is not that their PCs are ungainly -- some are, some are not -- but that users are both beguiled by the holistic experience they get from Apple and entranced by the new style of post-PC computing that the iPad, iPhone, and Android represent.
PC makers have long been able to counter the all-Apple benefit by offering a much more diverse set of software and hardware offerings with which users can fashion what they specifically need -- a battle between customization and completeness. But we're long past the days of people assembling their own PCs. Plus, the common software needed are now available on both OS X and Windows (directly or via the cloud), so the value of that heterogeneity is less. In a world where a PC and a Mac offer largely the same capabilities, the user experience advantage of OS X matters much more than it ever has.
Additionally, PC makers have no idea what to do about the post-PC attraction that favors iPad sales over Ultrabooks, much less standard-issue "bricks." Ultrabooks have not sold well, as users opt for the real thing (a MacBook Pro or MacBook Air). At the same time, Microsoft's attempt to create an operating system that serves both the PC and post-PC worlds -- that is, Windows 8 -- is an awkward, "Frankenstein" platform. I strongly suspect users will reject it.