Quite. Analog or not, cables carry a lot of technology these days.
To attribute this to some DRM effort is quite a large assumption. I wouldn't recommend writing off a company like Apple based on an assumption like that, considering it is almost certainly not true.
Granted, Apple does not usually go out of their way to make sure 3rd party accessories are supported on future devices. They can be a bit reckless about modifying interfaces, which tends to accidentally break 3rd party products (which Apple doesn't even always know exist). Heck, they frequently break compatibility with their own older products.
I think there is a tradeoff here, though. MicroSoft is actually darn good at backwards compatibility, and Apple is good at innovation. Striking the balance is tough.