Apple is a company that is surviving due to its aggressive marketing, the elitist inclinations of its existing customer base, and its divergence into online music. Macs have now lost the technological edge in the digital NLE industry (underscored by the amount of PC technology they've currently adopted). In other words, MACs are now conventional, while PCs are revolutionary. This is why I believe there is no possibility of Apple gaining significant market share in the personal computer arena. Conversely, I predict an irreversible erosion of its market share, as more and more Windows solutions eat away at all MAC's traditional niche markets.
The desktop NLE market clearly demonstrates this. As the cost of top-notch professional systems fall to $3000.00 or less, the market growth fueled by an abundance of new NLE software releases reside squarely on the PC side. The challenge to Apple's own marketing is significant. Apple now has to rely solely on Final Cut Pro to maintain their NLE status quo. The problem with this is that FCP just doesn't stand out compared to the PC 'heavy hitters', Vegas, Premiere, and Pinnacle Edition. Therefore there isn't a very compelling reason for the new generation of NLE editors to choose MAC over the cheaper and more prevalent PC solutions. While there will always be the 'old school' editors clinging on to their favorite editing platform which they adopted years ago, a new uncommitted generation of editors are emerging, having grown up in a Windows environment, discovering that there's no real reason to switch platforms to ply their trade. As you point out, Adobe, the NLE software leader, has abandoned Mac as a NLE platform, Therefore, within the NLE niche market, any operating system migration will overwhelmingly be from MAC to PC rather than the other way around.