Question is do they need their own software to sell the hardware? Lets just say for the sake of argument the majority of iOS users start using Google apps across the board and throw Apple apps in an unused folder. Does Apple care as long as people keep buying iPhones and iPads?
To answer your first question.
Yes they do, very very much !
Because, yes Apple make wonderful quality hardware design.
However, the thing is, the fact that they have this huge "differentiator" in iOS and OS X that nobody else can offer in the market, enable them to sell premium hardware products.
Ultimately, the biggest problem Samsung, Dell, HP, Motorola, Sony have, its not that they cannot build well made hardware, it's that they cannot sell it, because peoples always end up compromising on build quality if you can save some money and still get mostly the same software experience.
Peoples are able to enjoy the difference in hardware quality, but more as an added "bonus" for getting a premium product than something you actually choose to pay extra for.
Having their own software ecosystem make Apple products in "another league" by default. Peoples accept to pay more for well made premium product because there is no other way into their ecosystem.
Remove that software difference, and suddently every sale Apple has to make will always include a comparison with tons and tons of cheaper products that are now way "closer" in term of similarity because they offer the same OS.
And Apple would sooner or later be "sucked into" the infamous "race to the bottom" that plague the rest of the hardware industry.
Right now, all other vendors would kill to get a software situation like Apple is in.
