"For instance, IBM now has about a 90% share of the mainframe market, but mainframe sales account for just a fraction of IBM's total revenues and profits."
Look at how much of the rest of IBM's revenues come from services related to mainframes. A significant part of IBM's service and support revenue is tied directly to IBM's mainframes -- a bit like Microsoft's Office, which isn't a core product, but it's tied to Windows, and it's part of what makes Windows profitable.
What differentiates IBM's mainframes from the few remaining competitors (there are only something like 10 companies in the world in that space) are advantages that Windows has no analog for -- Windows' biggest advantage right now is, comically, Windows (i.e. market share).
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"For instance, IBM now has about a 90% share of the mainframe market, but mainframe sales account for just a fraction of IBM's total revenues and profits."
Look at how much of the rest of IBM's revenues come from services related to mainframes. A significant part of IBM's service and support revenue is tied directly to IBM's mainframes -- a bit like Microsoft's Office, which isn't a core product, but it's tied to Windows, and it's part of what makes Windows profitable.
What differentiates IBM's mainframes from the few remaining competitors (there are only something like 10 companies in the world in that space) are advantages that Windows has no analog for -- Windows' biggest advantage right now is, comically, Windows (i.e. market share).