See I say its engineering and market share, you say its just market share..
Nope, you're mixing apples and oranges and forgetting about pineapples. The biggest factor of them all is operations. If you don't properly manage your systems (UNIX, Linux, Apple, Windows, etc...) you're in danger of getting hacked.
Now if you're slow to patch you're more at risk if you're running an OS with a large market share because script kiddies will be able to exploit your box.