apple make there OWN PHONE AND OPERATING SYSTEM and ONLY HAS TO WORK ON 3 phone for update.
1-THIS YEAR MODEL
2-PREVIOUS YEAR
3-before that year
While true, that's barely relevant. The advantage Apple has (had?) over the carriers is bargaining power. Although that power is fading, the legal framework Apple worked out with the carriers hasn't changed. Google just couldn't care less about that angle of the business (which I think is their biggest flaw), and MS is too weak, meaning MS basically bends over whenever the carriers tell them to. That Apple could dictate their terms, and that those contracts are still legally binding today, is the true source of Apple's competitive advantage.
Even if Apple had 20 SKUs to update, they'd still have no trouble providing the same top notch update service they do today. It would be a bit more expensive, but I very much doubt that an extra two or three million would be enough for them to consider changing their update policies.
For the technically less inclined it's probably hard to fathom, but there really are only three WP models in circulation to worry about, so technically, MS' situation is similar to Apple's.