They don't need to take over the world, they just need a small slice to pay them a lot of money;
Why not have a bigger slice to pay them a lot of money?
Given your argument, we never would have seen an iPod for Windows, and we wouldn't see iPods and iPhones being sold at Walmart.
They don't need the straggling few who refuse to switch from V.
Straggling few??? I know a lot of people who would buy an iPhone on Verizon tomorrow if it were offered.
If they were worried about this, they wouldn't have signed a 5-year agreement!
I'm sure they only signed the 5-year agreement because AT&T was the only carrier willing to cede control of the device to Apple. No Apple control = no iPhone (and subsequently no flexibility of carriers on other devices (like Android) that we're seeing right now).
The iPhone changed everything in the mobile industry (despite what the deniers will wail), but it only happened because AT&T was willing to cave. The long-term contract was certainly the carrot on the stick.