Well, I'm using a French Mac layout and I can type ALL French letters, program and also type in Swedish using some Cmd+Key combo. Sure, I don't have the keys available right away, but it works. Also, on a Mac, Caps Lock really makes an uppercase letter, so it's easy to type an uppercase one with accent.
But typography rules use to say it was alright not to put accents on uppercase letters.
To that, you should add the fact that a LOT of people don't know how to write French properly and make tons of spelling errors when they write or type. I wouldn't expect most of them to care about any special characters or the proper uppercase letter!