Big companies can't risk going with a freelancer (who might go out of business or be booked when they need updates) so they put out an RFP to software firms.
A month or so of upfront design (wireframes, screen design, user stories). Another couple of weeks of iterations to get signed off by the branding/marketing group.
The development will need a team, four developers is about right (we need to get this app out fast in the ever-changing mobile landscape). We'll need a manager at half time and a team lead to handle client meetings. Throw in a dedicated test engineer (so many phones to test on these days...) and a month for formal test plans and execution (did we mention this app might be audited? test plan is 500 pages).
Make sure it is localized as well - we are a global company with global customers, all of whom we value. We also don't want to be sued, so we'll need a EULA screen that the user must accept. And a help page. And a way to register on our site.
Oh yeah, the way our budgets work, we've only got one shot at getting money for this app - can't do a minimal release and update it after it's in the store.
Conversative costs for an app in the OP's "BMW Tier":
One month upfront design at $100/hr (1 designer, 1 dev): ~$30k
Three months of development at $100/hr (4 dev, 1 test): ~$250k
Three months for PM at $150/hr (0.5 PM): ~$40k
One month formal resting at $100/hr (1 test): ~$15k
Monthly maintenance/update 20hr/month (1 dev): ~$25k
Total: Over $350,000 for the version 1.0 of your mobile app (on a single platform)
Apps ain't cheap.