We've known for like Google does and can treat the same URL but with different cases differently. So domain.com/Apple vs domain.com/apple can be seen by Google as different URLs. But Google seems to be stricter about this rule when it comes to the robots.txt file.
With domain.com/Apple vs domain.com/apple, Google can tell if the pages are identical and will canonicalize the URL to one of them, so both won't show up in search and Google may consolidate the signals as well.
But maybe if you have a robots.txt directive for domain.com/apple but not for domain.com/Apple, Google may not use Robots directive?
John Mueller from Google posted video on URL case sensitivity and at the 1:08 mark said "another place where the exact URL plays a role is robots.txt. In the robots.txt file you can signal which parts of a website shouldn't be crawled. The robots.txt file also uses exact URLs. So if you have entries there which refer to one version of a URL, they would not apply to other versions of that URL." John did add that it is "rare that we see this cause problems though."
So keep this in mind not just for overall how Google may canonicalize your URLs but also for robots.txt handling.
Forum discussion at WebmasterWorld and Twitter.
