Not even counting Wizards, whose only real advantage over the Mage build these days is free Ritual Casting and a few free rituals at various levels. Otherwise, the Mage wins with an extra at-will and better class feature bonuses.The main reason is that some classes are balanced in part on the idea that they do get ritual casting for free (such as the Bard or Invoker). Now, if none of your players are playing a class that gets ritual casting for free, then there's really not an issue. But those who are will in essence be getting short-changed when you hand it out to other classes. In other words, Bards no doubt did not get some other ability, feature, etc. because they DID get ritual casting.
My motivation for giving Ritual Casting is to promote it. For those who might be taking a loss, we'd decide whether or not an additional boon might be in order, such as enhancing their Ritual Casting.
My experience so far has been that rituals get underutilized...and since they tend to evoke pre-4E spell systems, I'd like to encourage their use. Obviously, this would be a campaign-specific house rule.