Yes they do pretty much some of the same things. However, its all about data portability.
You contacts and other information should always be able to go with you where ever or what ever you go to.
iCloud at this point in time only works with apple products.
You never know down the road if you may get some other non apple device like an android something else. When/If that happens you just plug in your google account info into whatever new device your using and all your contacts and info is pulled in.
google also has the option to simply download all of your information that you have in all the google services to have for safe keeping or incase you just want to move on to some other service.
Its sort of like the discussion about having Mp3's vs apples DRM AAC format.