iPhone example; Apple had tons of experience selling iPods first. They had probably learned that users desired more functionality, they would pay for it. The iPod became a device people would carry everywhere. So it made sense to combine it with a phone, which people also wanted to carry everywhere. (The phone was the iPods biggest threat.) Now, how to design it is where you get to be creative and where Apple excelled. Also, I think them partnering with AT&T (I think) to ensure proper network availability helped them out. Otherwise, people would have just complained that it cost too much for data. This was already a big hindrance in the US market for any type of smart device. Point is, Apple through the iPod had a good idea that the iPhone would be a success if executed properly.

Netflix example; because of their DVD business, they knew users wanted on-demand. Mail was a bottleneck. So they had a pretty good idea their customers would see the benefit of streaming.

As you mentioned, new ideas are tougher because you can't learn from your existing customers. There's no simple answer, but you just have to formulate a strategy. Target a particular segment that "get's it". Take it one day at a time. Some things are only possible with enormous resources. If you can't find the resources, it's not possible and you should move on.