They can only diverge so far though. For example, Apple needs a reasonably sized slice of the pie to maintain the App Store. If they had 0.1% of the market, there would be drastically fewer people willing to write apps.
Another thought- market share is often desirable not only for profit, but influence in that market.
Clearly Apple has demonstrated you do not require market dominance to influence or even drive the market, but their success in that regard does not appear to be easy to replicate.
Large market share might also lead to more stable profits, though I'd want to look at empirical evidence before saying for sure. Large profits on small market share reeks of an unstable situation, because at least in theory very high margins shouldn't be stable in the face of functioning competitive markets. My guess would be that high profit margins can evaporate overnight more easily than large market share can evaporate overnight (look at how long AOL has been cashing in on the very slow draw-down of its once-large customer base). Though it probably depends on how fast the market typically turns over. On the other hand, arguably Apple is in something of a luxury goods segment, and economists have long recognized that luxury goods operate in strange ways when compared to "normal" neoclassical markets.
Yes, but AOL is a subscription service. Phones last 2-3 years tops. In that time frame if your product is made obsolete you can lose your pants overnight regardless of whether you sell 10s or 100s of millions of units today. Large marketshare is no guarantee of anything in the fickle tech world (look at Nokia), so I'll take profit over marketshare.
It should be noted, however, that many reports have concluded that Apple-customers are (much) more likely to pay for software and apps. This certainly plays a role in which platform developers choose, assuming they want to make money this way.
