I don't think anyone is excited to buy gas at $4 a gallon, but that doesn't make it an unprofitable business to be in. MS has been running with out it's founder for years and has been moderately successful.
If one is to believe the reality distortion field that Jobs is central to Apple's success then his health problems pose a major problem to the long term value of the stock.
Apple has some very serious competitive risks (Android) and some very serious internal risks (Jobs' health). Apple's stock price is based on the idea of maintaining 30% growth for the next few years, that's a much more difficult goal than to lose 2% per year. Also, Moore's law is still relevant in the mobile market meaning that people replace their phones fairly frequently to get better hardware support. A mobile phone from 5 years ago is clearly inferior to most people whereas a computer from 5 years ago is mostly adequate for most users. What this means is that there is still time in mobile for a major competitor to emerge. The desktop PC market is locked up and belongs to Microsoft. The desktop PC running Windows is also a core part of the business to a lot of companies in the same way that Mainframes are to the financial industry. Yes, Microsoft's Desktop PC business will continue to decline for years, but it's a steady essentially risk free revenue stream. The mobile revenue stream is still largely up for grabs.
Microsoft also has big inroads into enterprise sales which could solidify WinPhone 7 in the enterprise which would bring in some pretty big bucks.