Earlier quoted context omitted.
To whatever extent Apple has a monopoly on Apple customers, the same can be said for essentially every other company, making this a meaningless statement.
I don't think so, because to a very real extent there's a solid core of Apple fans whole will not leave the company's products, no matter how shoddy, no matter how buggy, no matter what. Granted, not everyone is a John Gruber making silk purses out of sows' ears[0], but many folks simply don't consider anything other than an Apple iLife™ to be worth living — never mind that Jonathan Ive's stuff isn't terribly attract…
This is pretty much irrelevant because this core is too small to support Apple. Apple very much needs to sell to the masses, outside their “core”, to keep afloat.