I've never heard them claim that. The claim is that for an appliance like a phone - rather than a general purpose computer - device reliability trumps all, including the ability for the consumer to run arbitrary code on the device.
> Opening statement from Apple CEO Tim Cook
> When the App Store was created, the prevailing distribution options available to software developers at the time did not work well. Brick-and-mortar stores charged high fees and had limited reach. Physical media like CDs had to be shipped and were hard to update.
> From the beginning, the App Store was a revolutionary alternative.
> App Store developers set prices for their apps and never pay for “shelf space.”
[...]
> [Apple’s commissions] are vastly lower than the 50 to 70 percent that software developers paid to distribute their work before we launched the App Store.