That point is a clear but unrelated piece of strategy. Apple doesn't want Flash for myriad reasons before you even get to "maybe people wouldn't build as many native apps."
I think you'd get a chuckle from the Apple brass if you asked if they were worried that people would stop building apps if only they had access to Flash. Of course they wouldn't — the UX and fiscal rewards are unbeatable.
Apple creates lock-in all on their own by providing a solid set of developer tools and APIs, along with UI/UX patterns that work really well. You get some great stuff on iOS that's tough to build, and so tough to find, elsewhere. Flash wouldn't change that — it's general purpose, not specialized to the platform.
It's a bit like saying you don't eat sewage because it's bad for your health. I mean, that's true, but the real reason you don't do it is because you find it revolting to the senses. Apple may enjoy strategic benefits from their Flash stance along the lines of what's been described here. But their opposition to it comes from much more high-level, basic concerns.
