TM was a hack - iCloud is pretty good I reckon - for the millions of devices they have in the market there has been the only odd complaint from somebody on twitter making headlines with a Technorati type of following about user accounts mysterious being deleted or blocked (poor customer support) or some weird syncing issues when moving to a new device and the old device is still in use.
A local copy is inherently fragile. It's easily destroyed by accident, flood, fire etc. This is especially true when using a single storage device like an SD Card, vs the way that these storage services operate, leveraging things like erasure encoding.
Local backups are important, they're cheap, and often fast. They just shouldn't be the only kind of backup you do for data that is important to you.