I don't know how I feel about being able to use ritual scrolls without training.. it seems like it trivializes the whole process. It seems to blur the line between life and death even more than in previous editions when even the equivalent of a 1st level commoner can raise the dead with a scroll and one easy payment of 499.99, allow 8-10 minutes for delivery (granted 500g isn't so easy to come by). Guess its part of that 'gamist' philosophy all the kids are talking about these days. Damn kids and their music.
No, skill training is what you want to maximize your chances when casting a ritual - to get the best possible result.
Unless specifically noted, you don't need "training" to use a skill.
The point is, any Paragon tier character is at least as good at *all* skills as a level 1 trained character. (The +5 you get from training is equal to the +5 you get for being 11th level)
Require training and you shut out a lot of classes from, say, Raise Dead, bringing back the spectre of 3E, where a Cleric was
required, simply because noone else had access to the Raise Dead spell...
If you wish to "detrivialize" the process, my suggestion is instead to introduce skill checks for more rituals, again making which skills you're trained in more relevant.
In the case of Raise Dead, perhaps your skill check could govern how many milestones you need to pass before getting rid of the death penalty, or something...
This would still leave the Fighter able to use the ritual, only that everyone would prefer it if he didn't...