There are certainly much worse bugs than $100k. Think of if Apple itself had been hacked due to a bug. The remediation costs would be very high.
A bug in Knight Capital's stock trader lost $460M in 45 minutes.
A bug in the Ariane 5 rocket caused it to crash, a loss of $370M.
A bug in the Therac-25 radiation machine killed 3 people.
> secret features left open from the beginning?
Are you saying Apple engineers are inserting backdoors? What's the motivation? Security bugs are very easy to accidentally introduce when you have complex interacting systems (in this case a browser, a complicated URL parsing syntax, some ancient barely-known file types, and a file sharing application). Occam's razor (and Hanlon's) says it's an accident.